Sharing experience of an issue:-

NSD will show this fatal thread:-
{
################################################## ##########
### FATAL THREAD 33/140 [ nBES: 272c: 20cc]
### FP=0x2b4cf070, PC=0x60176a81, SP=0x2b4ce8fc
### stkbase=2b4d0000, total stksize=36864, used stksize=5892
### EAX=0x01e40648, EBX=0x00002ffd, ECX=0x01880000, EDX=0x01880000
### ESI=0x2b4cef04, EDI=0x017e8fe5, CS=0x0000001b, SS=0x00000023
### DS=0x00000023, ES=0x00000023, FS=0x0000003b, GS=0x00000000 Flags=0x00010206
Exception code: c0000005 (ACCESS_VIOLATION)
################################################## ##########
@[ 1] 0x60176a81 nNOTES.Panic@4+417 (60ae2948)
@[ 2] 0x6000294d nNOTES.LockHandle@12+317 (2d52,2b4cf09c,2b4cf0a8)
@[ 3] 0x60002776 nNOTES.OSLockObject@4+22 (60dd5c60)
@[ 4] 0x6002b077 nNOTES.IDHTableValidate@8+247 (0,0)
@[ 5] 0x60025e5a nNOTES.OSMemIDTableDestructor@4+26 (2ffd)
@[ 6] 0x60008ac0 nNOTES.OSMemFree@4+256 (2ffd)
@[ 7] 0x6050b877 nNOTES.ClientFolderGetIDTable@20+423 (0,1fd,8d6,0,0)
@[ 8] 0x60773850 nNOTES.iNSFFolderGetIDTable@20+128 (0,2b4cf280,8d6,0,0)
@[ 9] 0x607546e3 nNOTES.NSFFolderGetIDTable@20+83 (0,1fd,8d6,0,0)
@[10] 0x00668154 nBES.RIM_NSFFolderGetIDTable+148 (892834,16b9,1fd,1fd,0) @HandleChecker.cpp(1231)
}

IBM Reference: IBM - Access violation below SrvDbFolderGetIDTable

Remarks: Usually, the Domino mail servers where the BES users resides is 6.5.x.