validation help! -general entity "UserID" not defined

I get the error: Line 180, Column 35: general entity "UserID" not defined and no default entity

<li><a href="default.asp?PageNo=1&UserID=24&PageID=45;" title="Home">Home</a></…

Why?

is there a way out?

Replace '&' with '&amp;' throughout your querystring.

<li><a href="default.asp?PageNo=1&UserID=24&PageID=45;" title="Home">Home</a> Change all &s to its equivalent html entity &amp;