I just tried duplicating the problem in a brand new file and couldn't, so it must be related to some other setting or condition as well. Can't post the actual file where the error occurs, obviously, but I'll try and reproduce it with a junk file that I can post.
Whenever I try to copy a note in NX 6.0.4.3 that contains either <W@$SH_SHEET_NUMBER> or <W@$SH_NUMBER_OF_SHEETS> (and possibly others that I haven't tested), I get the following error message:
Enter Drafting Application
Error recovery completed for the following error:
An illegal file was...