Vista - 64-bit Vista Bussiness, Error = 216

hi
We have a product that works with windows 32-bit version of OSes. Now we are about to support the 64-bit OS. We didn't do any changes to software and knowing that 64-bit OS can still support 32 bit applications.

The software works fine on 64-bit Vista Ultimate and throws error on 64-bit Vista Business edition. We performed this tests on two machines and they have same hardware configuration. Only difference is the OS.

Software that we developed communicates to external device using USB TO serial (COMM) interface.

Every time the software tries to communicate to USB to serial interface i am getting following error message.

Error running "C:\program files(x86)\...\COM_HOOK.EXE" Error = 216.

It appears that meaning of the error code is ERROR_EXE_MACHINE_TYPE_MISMATCH.

If the exe type is mismatching how it is working on Ultimate and throws error on Business edition.

I even did the windows update on Business edition and reinstalled the USB to serial interface driver. Still I got the same error. Looks like I have to do some update on vista business but I don't know the exact update. Or am I still missing the details?

Thanks in Advance.
HJM