Tried it and it makes no difference.
I've tried everything I can think of right down to clearing everything off the PRS600 and starting from scratch. The 'About' on the reader clearly states 'This device is authorised for Adobe DRM protected content' and the odd thing is that sometimes I can read books from my local library and sometimes the protected page error appears. I can ALWAYS read them from the SD card via my PC.
The 'Tips & solutions' page on the Sony site gives a 2 step solution:
1. Delete all borrowed books from the read and transfer them again from Adobe Digital Editions or eBook library
2. Verify that all the borrowed books are of the same format (ePub or PDF) before transfering them to the reader.
I've tried this too - even deleting every book on the reader including all the free ones - and the same problem occurs.
Any more suggestions ???