Have you multiple data streams enabled also in the policy?

The data streams are created before the exclude lists are read, so a job will be created before nothing is subsequently backed up - used to result in EC=71 but I s'pose EC=90 also matches somewhat?

*If* this *is* the case then the only way around it would be to disable multiple data streams in the policy, or specify exactly the drives you want backed up in the backup selection & forgo exclude lists.

I:\*
F:\*
is the correct way to exclude contents of drive letters.

See this TN: http://www.symantec.com/docs/TECH125205