I'm would hope that this problem has been resolved by now, but I thought I would throw in a few pennies for current and future readers.
Along with what has already been described, I have seen the glue that holds the coil in the brake loosen after extreme temps, causing this same problem. Very difficult to diagnose, since most brakes are cooled down by the time a tech arives, or maint allows them time to cool, so they can work without being burned. NOTE: This time lapse allows the coil to settle back into place, since the brake is mechanically applied. Hence, allowing the brake to appear as normal.
Agree with Raytech, Check the wiring circuit associated with your brake. I have had a couple new trucks where the brake was engaging and disengaging during a work shift (with deadman depressed) and went on like this for about a week till the wire finally broke completely and entire brake system, pad, rotor, electric magnet got toasted after the operator drove it acrost the entire warehouse. When this first occured I couldn't figure out why it was doing what it was doing but after it finally failed completely we figured it out and know what the signs are.
Since the raymond motors move and all the wiring connected to them moves, the wires break. Especially where the wiring is firmly tied down with zipties and one side is moving back and forth all day long.
You dont mention how old this is, but it's electric brake correct? Did you measure the voltage at the brake plug when the failure occured? If it's got battery voltage but still tight, the brake unit is toast. You may need a relay as well..
The brake may be on due to loss of voltage from broken wires, usually where the harness twists.