The one book I got at Fictionwise works perfectly. Then I tried some from ereader.com. I have downloaded the latest reader software and I bought a book today to update the credit card on all the previous purchases.
One book converted fine. Another one gives me this error message:
Error: Invalid File Format (Merriam-Webster Pocket Dictionary bought in 2007 for about $30).
Another one gives me this error message:
Error: Incorrect eReader version 10 (error 1) (ereader.com BestSellers sampler bought in 2007).
Help? Thanks!

I mostly buy at Fictionwise but I'm worried a future purchase there will give me the same error than ereader's purchases, so I want to learn what's causing those errors.
P.S. I had a total of 6 ereader files... 4 of them converted no problem. The other two gave the error given above.