Just started noticing the same issue today "null tag error" when I copied some surface contours. I believe they were using Streamline as the drive method. I'll double check tomorrow at work. Sounds like a GTAC issue to resolve.
We had issues with the base install of NX6 with the copy/paste operations of planar mill routines. Having the floor plane defined caused the operations to crash during copy/paste. The work around is to clear the floor plane, then copy/paste the operation, then re-define the floor plane in the source operation after the copy/paste operation is completed.
If you are allowed to upgrade your NX6 install, upgrade to the latest maintanence release 6.0.2.8. I hope this helps.