Cannot start process on Windows7

Hi,
I am looking into bizarre problem: cannot start application by double clicking on it (cannot run it as a process) on bunch of Windows 7 machines. The same application when registered as service runs just fine.

the application itself is ATL server - runs fine on WinXP-Win2003/2008/2008 R2/VIsta and some Windows 7 as well.

When it runs as a service I use the same credentials as logon credentials when running it as a normal process. UAC is disabled. Running process with option runAs Administrator doesn't help.\

Account I use is in local admin group.

If I try to debug it from VS I see that "Access Denied" exception is thrown well before it even gets to any of my code - somewhere in ATL.

Any ideas where should I look? Any help is appreciated. I am out of ideas.

thanks
Lena