I was getting this error in Visual Studio 2005 when starting the debugging (running) a project:
Because of this error I wasn't able to edit the source code while the application was running in debugging mode.
And also looked and tried other threads on the above site and other forums, but at last solved it by manually removing the files in debug directory and then also removing the solution's .SUO file.
I have windows 7 64-bit with Visual Studio 2005, and my project was containing Crystal Reports. I had to set the target CPU type to x86 from solution property and from project property for Crystal Reports to work.
The problem could have been occurred because of target CPU type and/or opening (just opening, not edited) the .SUO file in Notepad to solve the Crystal Reports problem. I had to set the CPU type to x86 because my OS is x64 and Visual Studio will, I think, create an x64 exe, but the Crystal Reports installed on my computer is not for x64 and thus while compiling/running the project, a runtime error regarding Crystal Reports was generated