Normally on these Traigo 48 its people not pressing / holding the release button in before they pull the lever down to release the parking brake.

What then happens is the cable stretches & wont allow you to release the parking brake.

There are adjustors for the cable at each end.

I've yet to see or hear of a broken parking brake cable on one of these Traigo 48's

Send me an email over & ill send back the info on how to check & adjust the parking brake.