Just found this thread
I used the same topic as was posted on XDA Devs when updating my P3600 over Win Vista Home Premium, and following the instructions to the letter, the update worked OK. I had alredy updated WMDC to V6.1 which didn't allow native RUU updates as has been suggested by some users.
After the ROM update, one thing that drove me to distraction was that WMDC would not create a partnership with the newly flashed P3600. Most of teh time, it didn't even acknowledge the USB connection, and when it did, it got no further than 'Attemping to connect' reagrdless of whether RNDIS or Simple connections were enabled on the P3600 (USB to PC)
Eventually I decided to go in to Device Manager (on one of the occasions when at least the device was showing as connecting) and delete the HTC USB Device entry. I then ran Windows Update which proceeded to tell me an updated driver was available. It then downloaded and installed the Vista HTC USB driver, and from that point all went well again, and WMDC ran properly.
So, in my case at least, the spoofed ActiveSync Driver needed to be replaced by the genuine article to allow a partnership to be set up and run. Presumably I'll need to rerun the whole process again next time I update the ROM, unless MS get off their *rses and fix the problem properly.