Why does UserPrincipal.FindByIdentity return an error about GUID being 32 bits?
<p>My application uses the <code>UserPrincipal</code> class to determine what groups a user belongs to and then uses that information to determine if a user is authenticated to use my application. Things worked just fine for while, but recently I've started getting an exception</p>

<blockquote>
  <p>Guid should contain 32 digits with 4 dashes (xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx)</p>
</blockquote>

<p>When calling <code>UserPrincipal.FindByIdentity</code>. It seems like the call is succeeding and the exception is being handled properly, but it makes me nervous that authentication is going to break suddenly in the future. I'm not explicitly creating the GUID anywhere, so I have no idea where the exception is coming from.</p>
