You can deDRM any Mobipocket ebook. Only thing you need to know is one of the PID with your ebook has been locked.
Once you know the device PID (or the PID with you purchase the ebook) you need to get mobidedrm.py. There are some versions available. Surelly one of it will work. That program will take your ebook, your PID and generate a non-DRM ebook.
For the Kindle/iPhone/iPod, PID is scrambled into Device serial number, then you need kindlepid.py to obtain your PID from serial number. Once you have it you can deDRM your Kindle ebooks as explained.
Those programs can be found in Internet. Google is your friend.
