Green light stuck on (intermittently)

[ac22]

I have a BMW phatbox with a modded DMS cartridge that intermittently turns unresponsive. 
I modded a 120 drive to use for my DMS cartridge and it appeared things worked correctly, everything booted up and played for several days, then one day I turned on the phatbox and I got a "check CD error" on the head unit and a solid green light on the phatbox. 
That green light stayed on even if I turn the head unit off and/or removed the DMS cartridge.  The only way I could get the light to go off was to disconnect the adapter cable and power off the phatbox.  After I do that things will work for a few days and then the same problem will pop up again.
I'm not really sure where to start diagnosing this problem, is there a problem with the DMS cartridge or the phatbox itself?
Any help is greatly appreciated.