That error would seem to indicate that thread 43279 (in XF) has multiple polls. Threads are not allowed to have multiple polls in XF. Do you know if this thread has multiple polls in IPB?
Or this may be the result of you selecting the option to preserve the source ids at the beginning of the import. If you preserve the ids while importing into a populated database (already has threads, users, etc) then you can get these duplicate entry errors.