Why can't I run an exe with a specific filename?

I have recently encountered a problem on my Windows 7 machine where I can't run an application with a specific name. Let's call it a.exe.

It is a C++ Qt based app and has been working OK for months but when I tried to run it today I got "The application was unable to start correctly (0x80000003). Click OK to close the application.". This happens for both 32-bit and 64-bit builds for Debug or Release.

I spent hours going round in circles checking dependencies and rolling back to previous versions without getting anywhere. I tried the software on a different machine and it worked, so it must be something on my machine...

I finally discovered that if I rename it to something else (e.g. a1.exe) then it will work :-S

I've checked the VirtualStore folder but couldn't see anything. Any other ideas?

Maybe your "known file extensions" are hided, and you are trying to access a.exe when actually the file name is a.exe.exe?