500 DECT Not Registering

[Cheque]

Hello,
I have a 500 DECT Handset that had been connected to the network for at least a year. However, a few days ago it lost its network connection while on a call and did not connect back. I thought deleting the registration and registering it again would solve the issue, but now it won't even register, I keep getting the "DAP Error" message. I have some 8232s, 8242s and a 8262 connected to the network and I didn't have any issues registering them.

Any ideas as to why the 500 won't register?

Thanks