<p>I have a ASP.NET application running on a remote web server and I just started getting this error.  I can't seem to reproduce it in my development environment:</p>

<pre><code>Method not found: 'Void System.Collections.Generic.ICollection`1..ctor()'.
</code></pre>

<p>Could this be due to some misconfiguration of .NET Framework or IIS 6?</p>

<p>Update:
I disassembled the code in the DLL and it seems like the compiler is incorrectly optimizing the code.  (Note that Set is a class that implements a set of unique objects.  It inherits from IEnumerable.)  This line:</p>

<pre><code>Set&lt;int&gt; set = new Set&lt;int&gt;();
</code></pre>

<p>Is compiled into this line:</p>

<pre><code>Set&lt;int&gt; set = (Set&lt;int&gt;) new ICollection&lt;CalendarModule&gt;();
</code></pre>

<p>The Calendar class is a totally unrelated class!!  Has anyone ever noticed .NET incorrectly compiling code like this before?</p>

Is your IIS setup to use .NET 2.0?  If not, change it to 2.0.  If you can't see 2.0 in the list then you'll need to run aspnet_regiis from the 2.0 framework directory.