My environment:
OS: Windows XP
Web Server: IIS 5
.NET Framework: 1.1
IDE: Visual Studio 2003

After moving or copying my code directory, when I tried to open the solution in the Visual Studio 2003, I got an error: "Unable to get the project file form the Web server" as following screenshot.

The reason is the Visual Studio cannot open the project file, which is http://localhost/projectName.csproj. I checked all settings of the IIS and permission of files and found nothing was wrong. After several hours struggling, I finally figured out following solution.

I deleted the all files under VSWebCache folder which is under C:\Documents and Settings\my_user_name\. The screenshot is as below. The possible reason is when I copied or moved the code folder, the previously generated runtime chache conflicts with the new code folder's location.