Patching Directions:
1. Get a Back-Up Master Base.
2. Put MWS in Deck Edit Mode.
3a. Click on the Library (Top Panel or Left Panel), save.
3b. Analyze/Add/Remove Sets
4. Add Rise of the Eldrazi with key ROE.
5. This should say added (some number of) cards.
6. Click a card in the left hand column (top), from the library, then go to File, Save Deck/Library.
7. Here it still wont work and gives the error. So close MWS, then reopen it. This seems to do the trick for me. Sorry if this is patronizing but it's all I did.
To download the ROE Patch, go here and download the txt file. Follow the above instructions! Voila!