It sounds as if the firmware has corrupted the set.
Details:
Unable to access any overlays on call server, OVL306 given on TTY. This was the result of a failed FDLU to an M3903 telset in my case, I suspect pertinent to all M3900 range of phones however.
After accessing load 32 by using the suspension command and an FWVU is run against the affected TN you get 'PSDL IS NOT IDLE' message
Fix:
Use the suspend command to access ld 32, use fdlc to cancel the suspended command, disable & enable the affected card and re-commence a subseqent FDLU.
This time, in my case, the download was successful.
This particular set in question was served of a Remote Gateway 9150 and it is possible that the set did not respond quick enough to the request for download in the first instance which caused the download to fail on first attempt.
All the best
Firebird Scrambler
Meridian 1 / Succession and BCM / Norstar Programmer in the UK
If it's working, then leave it alone!.