Benny Abergel was kind enough to share the following valuable QTip with us:
QTP can work on 64 BIT OS with one big limitation - 64bit application cannot be recorded/replayed. QTP will work only on 32bit application (many of the AUT can work on 64bit but are actually work on 32bit mode – can be noticed by the * in the task manager).
Many developers are creating the application to work on both 64bit and 32bit (the application will work 64 on 64 bit OS and 32 on 32bit OS), thus allowing us to use the following workaround, and still automate our AUT with QTP (this is relevant for .NET only).

The 64bit limitation can be overcome by using CorFlags.exe utility (included in the .NET SDK installation).
Usage: Corflags.exe <Assembly Name> /32BIT+
The utility will force the assembly to run in 32bit mode.

*many application written in .NET are compiled with Any CPU option(running 32bit on 32bit OS and 64bit on 64bit OS) , if you can compile you App choose the 32bit option to be always compatible with QTP..

Thanks Benny, for this valuable QTip. It will allow us to automate many applications that were thought to be untouchable by QTP.