Problems with Library DRM epub and pdf
I am familiar with the problem listed below since I got caught a second time, ARGGG
This time the solution was not so straight forward. I tried deleting the files with the reader, the pdf would re-load but still could not be read. I tried deleting it via the PC as a simple file delete, still no luck. Finally I deleted it from within ADE. The weird part is the book was no longer on the reader but ADE still listed it. When I deleted the 'ghost' book it read fine when I re-loaded it.
sorry about the muddy explanations...
There should be an edit to the WIKI instructions... delete the DRM pdf from within ADE.
You can borrow epub and pdf books from your library, but be careful to never have both epub and pdf library books on your reader at the same time, as there is a conflict and you will not be able to access them. A Protected Page! error occurs on the Reader when opening a borrowed book that is in the ePub or PDF format when borrowed Adobe DRM-protected ePub and PDF eBooks exist on the Reader at the same time. Follow this procedure to correct this issue: From Sony eSupport 
1. Delete all borrowed books from the Reader.
There should be an edit to the WIKI instructions... delete the RDM pdf from within ADE.
2. Verify that all borrowed books are in the same format (either ePub or PDF) before transferring them back to the Reader.