 <p>I have found in the past that there are 3 dlls you need to have the correct version of for debugging .Net.</p> <p>sos.dll mscorwks.dll mscordacwks.dll</p> <p>here's how I usually go about getting these dll's <a href="http://sjbdeveloper.blogspot.com.au/" rel="nofollow">http://sjbdeveloper.blogspot.com.au/</a>, although it sounds as though you are using a server based application which means you could possibly just grab them from your production box, assuming you have access to it, or a staging box if you don't.</p>