I downloaded an office chair block from CAD Block Exchange Network. I did not understand the 'Student Version...Plot Stamp' message when I put it in with a group of office furniture blocks I had collected. I soon realized what the message meant and deleted the block and purged. Now anything from that collection of blocks creates a 'Student...' plot stamp. What can I do to undo this? I can't afford to get rid of all the other blocks...they all seem to be 'contaminated'. Any help will be greatly appreciated.