First, look in the windows event log (app log). It will probably show a fastfail error message along the lines "NET Runtime version 2.0.50727.3053 - Fatal Execution Engine Error (7A035E00) (80131506)"."
To get more details on what caused it you can either attach another VS instance as a debugger and watch the debug output, or you can enable fusion logging since this is usually caused by assembly load errors.
One common cause of VS fastfails is a bug in .net 2.0 SP2 that is described in more detail here:
http://support.microsoft.com/?kbid=963676
Other workarounds (if the patch described in the MSKB article linked to above don't work) are:
1) Running "ngen /delete *" (with administrative privileges, from the .net framework 2.0 directory).
2) An add-in I wrote that loads all referenced assemblies (and allows you to tweak the load order) whenever opening a project instead of as-needed. You can get it (and the source code for it) from here:
http://www.huagati.com/ProjectLoader/download/HuagatiProjectLoader.zip