Today when i was migrating a 10.5 UC cluster to 14 during the CUCM subscriber migration after network validation, i saw a warning message on the screen..

“Critical Error”

“The installation has encountered a unrecoverable internal error. For further assistance report the following information to your support provider.

Unrestricted string is empty

The system will now halt.

Searching On Cisco Bug Tool, i found a Bug ID (CSCvy93918  ) similar to my condition.The work around mentioned was to reduce the CPU size to 1. But that didn’t resolve my issue.

After redeploying the, OVA PCD migration went through.

Hope this might help someone..