Hi Coscw,
It sounds like the DSC_dbg.exe file is already in use when you try to build the second time. Do you open the .exe file after you have created it? If so, do you leave it open when you try to build it the next time?
Even if you don't leave it open intentionally, something may have caused the operating system to hang onto the application. You can open the task manager and look for the DSC_dbg.exe entry under the Processes tab. If the entry is there but you closed it on your desktop you will have to use the program manager to end the task in order to rebuild the .exe.