You will need to uninstall activesync 3.7 and install activesync 3.5 back. Then the "upgrade" to WM2002 should work. Otherwise you will need to copy the rom to SD Card first and install it from there. I am not 100% certain how to do the latter. I believe that you open the RUU_CEv31440.exe using winzip and extract the NK.nbf file and copy it to your SD Card. I think that you then install the Card in your PPCPE and reset it while pressing the power button. It should install from there.
Somebody please correct me if I am being a blind person guiding another blind person.
Hope it works.

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PDAPhone Apprentice