Try re-seating the Circuit Switch Matrix (MC243BA) card (on the inactive plane) first. (Don't do it on the active plance) Following a successful activity switch then re-seat the other (now inactive) circuit switch matrix card.
If the problem continues, then as suggested replace the card. No Spare? Give Terry Cunningham a call at Dean Communications (800-451-2089) They're about $300.
How are you forcing the activity switch, from the front panel of the SX2000 or from the command line? If doing so from the command line, does it reply with any message (i.e., "WARNING SERVICE WILL BE LOST" ?
Dunno how to force an activity switch from the coammand line?
"ACT SW 1 1 2" (forces an activity transfer from plane B to plane A
"ACT SW 1 1 7" (forces an activity transfer from plane A to plane B
Note that you must wait (typically 5 to 7 minutes) between successive transfers. I personally recommend waiting 15 minutes or longer. Always watch the screen for the warning message about losing service. If it ever warns you about a loss in service, then cancel (type in "NO" in response to the confirmation prompt.
Original MUG/NAMU Charter Member