I was having the same problem, but after downloading the ActiveModeSync to my phone it worked. (Since I couldn't get my phone to connect to the PC, had to follow this option
Option 2: INSTRUCTIONS FOR INSTALLING ACTIVESYNC MODE CAB FILE
on to the PPC6700 & XV6700 from the Internet Explorer on the 6700
it will automatically install to the device- After install, Close all programs on the device
- Tap Start, then select Programs, and then Active Sync Mode
- Switch from RNDIS to USB, then tap OK
- Close all programs then Sync with your computer.