I have a Windows GUI app that I have set to run with Windows Application Verifier. In particular, I have App verifier set to trigger on invalid handle exceptions (code is 0xC0000008). When the application is run from the Cygwin console, it faults with an invalid handle three times. I can continue past them in windbg (or gdb for that matter) and the application launches. I think it is curious the invalid handle exception occurs three times - is it stdin, stdout and stderr that App Verifier thinks are invalid handles? My hunch is yes, they are. I did notice that if I run the GUI use run.exe, as in "run guiapp.exe", the application launches with no invalid handle exceptions. I am using this version of Cygwin 64 vapkay@US05117NB ~ $ cygcheck -V cygcheck (cygwin) 3.1.7 But it also happens with 3.4.6 Is this to be expected with a GUI app when run under a Cygwin console? I've never seen it until I ran with App Verifier. The GUI application is a Qt app. I check the Qt version we're using for use of and I don't see anything in the WinMain what would have to do with reading/writing to the standard IO file descriptors. Any ideas? Thanks, Tom