title: Url is not a valid virtual path
body: <p>I have a hyperlink that passes variables with it. This is generating using a combination of strings and server properties. However it seems to work with some variables but not others.</p>
  
  <p>If I pass the groupId and issuedMemberId then it's fine.</p>
  
  <pre><code>&lt;asp:HyperLink runat="server" ID="groupUrlLink" NavigateUrl=&lt;%# string.Concat("~/UpdateMember.aspx?groupId=", DataBinder.Eval(Container.DataItem, "GroupID").ToString(),"&amp;issuedMemberId=", DataBinder.Eval(Container.DataItem, "IssuedMemberId").ToString()%&gt; &gt;
  </code></pre>
  
  <p>However if I instead use a different variable, Effective date,</p>
  
  <pre><code>&lt;asp:HyperLink runat="server" ID="groupUrlLink" NavigateUrl=&lt;%# string.Concat("~/UpdateMember.aspx?groupId=", DataBinder.Eval(Container.DataItem, "GroupID").ToString(),"&amp;effectiveDate=",DataBinder.Eval(Container.DataItem, "EffectiveDate").ToString())%&gt; &gt;
  </code></pre>
  
  <p>I get an error:</p>
  
  <blockquote>
    <p>'~/UpdateMember.aspx?groupId=0032409901&amp;effectiveDate=3/31/2008
    12:00:00 AM' is not a valid virtual path.</p>
  </blockquote>
  
  <p>As can be seen in the error it is correctly using the value for the Effective date. This is the only thing to have changed though from the first example so I'm not sure why it isn't working now.</p>