Boss i ahve also experienced this once with tems kit and found that the Ater media was down from respective BSC to MSC.
Pls check and confirm whether this was the problem at the time of RACH error.
Its an UL channel and goes with BCCH i.e ur signalling channel should keep working(on air) in order to make this channel(request) to reach respective VLR.
If anything doesn’t work in between MS and VLR ,then this error can come even if BCSU,MCMU cards of respective BSC are over thresholds and also in very worst radio condition which is usually called Ghost error.