No more room for new records" is telling you the sad story, but now it seems we need to find out exactly which one of the needed resources has been depleted.
DNI Channels is one of the things which comes to mind. What does your DIM A F D form say about your DNI channels? If you don't have an unused available DNI channel then we're through before we start.
As for Multiline sets, "96 96" would suggest to me that all ports have been either assigned or reserved. If you're really "only using 55" then it should say "96 55"
Try _completely_ removing one by removing it from the DNI assignment form. Then try programming the AIM again.
You didn't mention, so I'll ask, what version of software are you running? AIM was introduced in LW29 Rls 3 (Q26.13.1)
You cannot have Off Hook Voice Announce programmed on the same set that you're trying to use with an AIM module.
The AIM (SIM2) module is only supported on Superset 4025, 4125 and 4150. In order to program an AIM on the 2nd channel, the first channel would have to be programmed as one of those 3 types of sets.
The set software needs to be at Rls 6.3 or later to support the AIM module. The FIRM KILL command given against the associated PLID (with the set attached) will reflash the set firmware. i.e., FIRM KILL 3 1 2 [enter] NEVER use the FIRM KILL ALL command.