[VE][65] Possibly a parser bug?

Validating http://www.ffw.com/default.aspx 
Error [65]: "document type does not allow element X here; missing one of
Y start-tag" 

I'm sure I'll get put in my place if this is not a parser bug, however
I'm getting an error on this code:

<form method="post" action="/Default.aspx" id="aspnetForm">
        <div>
        <input type="hidden" name="__VIEWSTATE" id="__VIEWSTATE"
value="/wEPDwUENTM4MQ9kFgJmD2QWAgIDD2QWAgIBD2QWBgIHDxYCHgljdXJQYWdlTm8CA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" />
        </div>
 
SOME CODE
</form>

Error is:

Line 53, Column 1312: document type does not allow element "input" here;
missing one of "p", "h1", "h2", "h3", "h4", "h5", "h6", "div", "pre",
"address", "fieldset", "ins", "del" start-tag.

....9uc2RkFDJubKUtDBNaRSpXfZALHg9iSME=" />

However the code seems perfectly valid. I note that there is a "/" at
the start of the form value and that when this is removed, the error no
longer occurs.

By "removed" I mean that we have other web sites build with the same
content management system (Immediacy) that generates this code where
there is no "/" at the beginning of the form value and the error does
not occur.

Am I mistaken that this problem is caused by the W3C parser mistaking
the / for the end of the tag?

Thanks for any help,

Steve Attewell