I've tried to buy the Invocation of Azura book from Galbedir twice now, both times caused a crash as soon about a second after the purchase confirmation. What are the possible causes of this?
No crash buying it off Dorisa
No crash buying it off Dorisa in a new game. Guess I didn't avoid a problem when I added that lockpicking mod to an in progress game like I originally thought. Time for new game #7462.
Thanks for helping again Pr0

It may have an object script
It may have an object script which is making bad references... I'll do a quick check... Nope, no scripts associated with it. The NIF, texture or icon DDS file may be to blame. When I get a chance, I'll try to run Oblivion to see if I can replicate your crash.
Sorry, have not been able to replicate your problem. Of note, Galbedir does not have Invocation of Azura in her levelled lists, but Dorisa Darvel (bookseller across the street) does have it. I tried buying from her, selling to Galbedir and then buying it back. None of those actions crashed. Your problem might also be linked to your saved game. Try starting a new game and testing it again -- if it still happens, then it most likely is a corrupted NIF/DDS file.