I had this problem on a windows 2000 server I p2v'd. It was 2 processors on the physical box (dual core). When I made it a VM, it 2 vCPU as well. To set things right (I had weird CPU utilization showing on the VI Client vs the actual VM), I ended up changing the HAL to a single processor HAL and assigning a single vCPU to the machine.
Try changing your HAL in the OS (before) switching from 2 vCPUs to 1 vCPU. That should do the trick.
Have a look at this thread: How to repeatedly upgrade Windows 2003 to SMP and revert to uniprocessor
Wil| Author of Vimalin. The virtual machine Backup app for VMware Desktop Products
| Vimalin : Automated backups for VMware Fusion and VMware Workstation Professional
| More info at https://www.vimalin.com
| Twitter @wilva
| VMware Wiki at http://www.vi-toolkit.com