Modded leagues like ACFL (Formula 1 mods) or old SRS plugins sometimes use custom anti-cheat DLLs that specifically look for a hex-edit hash of acs.exe . If you have a legitimate v1.16.3 but the anti-cheat expects a modified one, you get the obsolete error.
Platforms like Sim Racing System (SRS) , World Sim Series (WSS) , and many community servers have updated their checksum and netcode to align with 1163. Older clients are blocked from joining multiplayer sessions. assetto corsa is obsolete v1163 is required fix