Note again that I haven't tried this myself and I don't know if this actually works. It was the proposal that I think got implemented but I haven't checked myself.
Edit: We are of course interested to hear from you which AI is it that you have problem with?
Thanks for advices - I'll try it (hopefully I use only 1 newest version of each AI).
Choochoo caused some errors (I send pm with screenshot to author already).
Some AIs didn't started yet but present AIs in game are: AdmiralAI.22 and CluelessPlus-v15 (AdmiralAI going to bankrupt again - probably due to Modified Building Costs grf and hard difficulty).
BTW *.gz files are read in the same way like *.tar by the game ?
Find new graphics easier:GRFCrawler