title: new Guid(string) is throwing a null ref exception but not when quick watched
body: <p>I have a pretty simple piece of C# code (it's a controller action in an MVC 2 that is called by the jQuery async post method). Basically I pass in 3 strings and do the following:</p>
  
  <p>var g1 = new Guid(string1);</p>
  
  <p>var g2 = new Guid(string2);</p>
  
  <p>var g3 = new Guid(string3);</p>
  
  <p>However on the 3rd guid creation I get a null reference exception. When I quickwatch the assignment it works fine, but when I just let it run I always get the exception (even when I change the order of the assignment or try doing var g3 = new Guid(string2); The strings passed in are definitely Guids.</p>
  
  <p>I am completely stumped as to why a simple Guid assignment would be failing, it seems like there is something else going on in the process that is causing this. Any ideas, or has anyone seen this behaviour before?</p>
  
  <p>Thanks.</p>