Today I came across a big problem with an obvious easy solution. I had just installed a new machine with IIS, VS6, VS2003 and VS2005 side-by-side. To Microsoft's credit, this works flawlessly. However, after getting some of my old VS2003 (.NET 1.1) projects from SourceSafe, I found I couldn't run the project in debug mode. At first I thought this was due to the side-by-side installation or an error in the installation, so I ran a repair on the VS2003 installation but found the problem persisted even after that completed successfully.
Turns out it has to do with the version of the .NET runtime the virtual directory is setup for. To solve, open Internet Services Manager, and open the Properties dialog on the Virtual Folder of the application in question. On the far right, you'll find an "ASP.NET" tab. Check the ASP.NET dropdown is set to the version of the runtime the site was developed in.
There are several other reasons why debugging may not work on your machine, but those are all documented in the VS help.
After 8 months of contract employment at Merrill Lynch, I finally converted to a permanent employee last week Wednesday (March 1st, 2006), Yay! I now get to enjoy such excellent things as career prospects, an end of year bonus (hopefully), benefits, sick days and paid leave. Great! Merrill Lynch really is a great company to work for and I look forward to the coming time with great excitement and expectation.