Inertia Seatbelt, Decided Its Had Enough

[Lloyday]

Afternoon, after fiddling about with a panel behind the rear seatbelt that had cracked the time came to re-assemble, although I had removed the seatbelt holder many times and had no problems with re-assembly, this time I found that the seatbelt's inertia lock has now trapped the seatbelt and It won't extend.

Does anyone have any idea how or why this happened and also how I can release it from the grip.

cheers :)