it means there are too many paging sent by the BSC to the BTS.
I’m not familiar with your “alarm”, so either the LapD (on the Abis) is congested due to paging, or the PCH (on the air interface) is congested due to paging.
You could try to investigate further, but a solution that would work in both case :
step 1/ ensure that one LAC is handled only by one BSC (one BSC can have many LAC’s, but one LAC should not be handled by several BSC)
step 2/ reduce the number of cells per LAC.