VirtualPathUtility.ToAbsolute problem

I'm using VB in VS 2010.  I have this line:
<a href='<%# VirtualPathUtility.ToAbsolute("~/ProductsList.aspx?CategoryId=" + Eval("CategoryID")) %>'><%# Eval("CategoryName") %></a>
I'm getting a :"Input string was not in a correct format." error.  What am I doing wrong?


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