The "normal" IIci does not use parity, so that should not be a problem. If it is a system that was in a high altitude area like snow mountain towns of Colorado or if it is a US Gov't system, then it would have parity circuitry. So lets assume that is does not have parity support... you need 4 of the same SIMMs per bank. At minimum you need Bank A filled, so all your SIMM Group testing must be done there.

Now, what kind of SIMMs are you using? And, you did the recapping? You checked the lines going to the SIMMs?