This question is very old so you have probably solved the issue, but just in case: Does the project file use IIS? If so then it is probably trying to read the project file from IIS and the virtual directory does not exist on the newly formatted computer. Also, there should be more detail about the message in the Output window when you open the solution which should help you find the cause. With VS2003, you also need to add your user account to the "Debugger Users" and "VS Developers" and possibly the account that is running the AppPool (possibly Network Server, ASPNET, or IUSER_xxx). This may depend on the type of authentication you are using as well. Occasionally I had to add those group permissions the the virtual directory location as well. It's been a while since I have used VS2003 with web projects though.