Bitte um Hilfe bei W3C Fehler (u.a. Ampersand-Fehler)

Hallo zusammen! Ich habe den GX2 installiert und bereits ein paar kleinere Modifikationen am Shopsystem erhalten. Nun habe ich meine Homepage (Ampirion Gamer PC Systeme) mal durch den W3C Validator gejagt und kam zu folgenden HTML-Fehlern. Könnt Ihr mir eventuell dabei behilflich sein, diese zu lösen?

Habe natürlich schon entsprechend gegooglet und bereits einige Fehler beheben können, aber diese bekomm ich leider nicht weg

Code:

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[*]      [I]Line 256,         Column 135[/I]:     there is no attribute "autocomplete"     …put-text box-input-field default_value" id="search_field" autocomplete=[B]"[/B]off" />                [URL="http://validator.w3.org/feedback.html?uri=http%3A%2F%2Fampirion.com%2F;errmsg_id=108#errormsg"]✉[/URL]     
                  You have used the attribute named above in your  document, but the       document type you are using does not support  that attribute for this       element. This error is often caused by  incorrect use of the "Strict"       document type with a document that  uses frames (e.g. you must use       the "Transitional" document type to  get the "target" attribute), or       by using vendor proprietary  extensions such as "marginheight" (this       is usually fixed by using  CSS to achieve the desired effect instead).     
            This error may also result if the element itself is not  supported in       the document type you are using, as an undefined  element will have no       supported attributes; in this case, see the  element-undefined error       message for further information.     
            How to fix: check the spelling and case of the element and  attribute,        (Remember XHTML is all lower-case) and/or        check  that they are both allowed in the chosen document type, and/or        use CSS instead of this attribute. If you received this error when using  the        <embed> element to incorporate flash media in a Web  page, see the        [URL="http://validator.w3.org/docs/help.html#faq-flash"]FAQ item on valid flash[/URL].
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[*]  [I]Line 537,         Column 38[/I]:     ID "FilterCategory" already defined     <select name="filter_fv_id[5][]" id="[B]F[/B]ilterCategory" class="input-select">                [URL="http://validator.w3.org/feedback.html?uri=http%3A%2F%2Fampirion.com%2F;errmsg_id=141#errormsg"]✉[/URL]     
                  An "id" is a unique identifier. Each time this  attribute is used in a document       it must have a different value. If  you are using this attribute as a hook for       style sheets it may be  more appropriate to use classes (which group elements)       than id  (which are used to identify exactly one element).
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[*][I]Line 524,         Column 38[/I]:     ID "FilterCategory" first defined here     <select name="filter_fv_id[4][]" id="[B]F[/B]ilterCategory" class="input-select">
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[*]  [I]Line 568,         Column 657[/I]:     cannot generate system identifier for general entity "XTCsid"     …" /> <a href="shop_content.php?coID=3&[B]X[/B]TCsid=6fb4e01eaae512ea1ce3bd337bb6f46c"…                [URL="http://validator.w3.org/feedback.html?uri=http%3A%2F%2Fampirion.com%2F;errmsg_id=338#errormsg"]✉[/URL]     
                  An entity reference was found in the document, but  there is no reference       by that name defined. Often this is caused  by misspelling the reference       name, unencoded ampersands, or by  leaving off the trailing semicolon (;).       [B]The most common cause of this error is unencoded ampersands in       URLs[/B] as described by the [URL="http://www.htmlhelp.com/"]WDG[/URL] in "[URL="http://www.htmlhelp.com/tools/validator/problems.html#amp"]Ampersands         in URLs[/URL]".     
            Entity references start with an ampersand (&) and end with a       semicolon (;). If you want to use a literal ampersand in your document       you must encode it as "&amp;" ([I]even inside URLs![/I]).  Be       careful to end entity references with a semicolon or your  entity       reference may get interpreted in connection with the  following text.       Also keep in mind that named entity references are  case-sensitive;       &Aelig; and &aelig; are different  characters.     
            If this error appears in some markup generated by PHP's session handling       code, [URL="http://www.w3.org/QA/2005/04/php-session"]this article[/URL] has        explanations and solutions to your problem.     
            Note that in most documents, errors related to entity  references will       trigger up to 5 separate messages from the  Validator. Usually these       will all disappear when the original  problem is fixed.
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[LIST=1]
[*]      [I]Line 568,         Column 657[/I]:     general entity "XTCsid" not defined and no default entity     …" /> <a href="shop_content.php?coID=3&[B]X[/B]TCsid=6fb4e01eaae512ea1ce3bd337bb6f46c"…                [URL="http://validator.w3.org/feedback.html?uri=http%3A%2F%2Fampirion.com%2F;errmsg_id=25#errormsg"]✉[/URL]     
                  This is usually a cascading error caused by a an  undefined entity       reference or use of an unencoded ampersand  (&) in an URL or body       text. See the previous message for  further details.
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[LIST=1]
[*]      [I]Line 568,         Column 663[/I]:     reference not terminated by REFC delimiter     …a href="shop_content.php?coID=3&XTCsid[B]=[/B]6fb4e01eaae512ea1ce3bd337bb6f46c" targe…                [URL="http://validator.w3.org/feedback.html?uri=http%3A%2F%2Fampirion.com%2F;errmsg_id=394#errormsg"]✉[/URL]     
                  If you meant to include an entity that starts with  "&", then you should        terminate it with ";".  Another reason  for this error message is that        you inadvertently created an  entity by failing to escape an "&"        character just before this  text.
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[LIST=1]
[*]      [I]Line 568,         Column 663[/I]:     reference to external entity in attribute value     …a href="shop_content.php?coID=3&XTCsid[B]=[/B]6fb4e01eaae512ea1ce3bd337bb6f46c" targe…                [URL="http://validator.w3.org/feedback.html?uri=http%3A%2F%2Fampirion.com%2F;errmsg_id=403#errormsg"]✉[/URL]     
                  This is generally the sign of an ampersand that was  not properly escaped for inclusion        in an attribute, in a href for  example. You will need to escape all instances of '&'       into  '&amp;'.
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[LIST=1]
[*]      [I]Line 568,         Column 663[/I]:      reference to entity "XTCsid" for which no system identifier could  be generated     …a href="shop_content.php?coID=3&XTCsid[B]=[/B]6fb4e01eaae512ea1ce3bd337bb6f46c" targe…                [URL="http://validator.w3.org/feedback.html?uri=http%3A%2F%2Fampirion.com%2F;errmsg_id=325#errormsg"]✉[/URL]     
                  This is usually a cascading error caused by a an  undefined entity       reference or use of an unencoded ampersand  (&) in an URL or body       text. See the previous message for  further details.
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[LIST=1]
[*]      [I]Line 568,         Column 656[/I]:     entity was defined here     …"" /> <a href="shop_content.php?coID=3[B]&[/B]XTCsid=6fb4e01eaae512ea1ce3bd337bb6f46c…
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