I opened up a solution today to be presented with a nice System.Runtime.Interop.COMException in Visual Studio 2008. After that my web project wouldn’t open.
After creating a new project from scratch and recreating I found a couple of ways to reproduce it:
- The project had been changed to an IIS project and all the IIS requirements hadn’t been installed on the VPC..so instead of a nice error to tell me what I’d done wrong..boom com COMException.
- After all the right things were installed, I’d forgotten to run Visual Studio as Administrator…boom COMException.
Hoping that’s all the combinations I find 
It’s not the nicest of errors and I don’t remember having that problem on previous versions of Visual Studio but then again, I haven’t run a lot of Web IIS projects on Vista lately. I guess the annoying thing about it is there’s no option to revert the project back to get it to open. When you first set the project to an IIS web project if you don’t meet the criteria it gives you a nice error and won’t let you save that option and reverts back.