After I got my new laptop, I installed among other things Visual Studio 2010. However, when I wanted to create a new GUID through Tools -> Create GUID, I got the error "Encountered an improper argument." from guidgen.exe : After confirming this dialog, the guidgen.exe window opened, but clicking on copy or New GUID resulted in the same error message: As I found out, VS2010 calls the guidgen.exe inside the Details