Can't change regions on a Sony BPD-S5500

[Bertaut]

A few years back, I purchased a multi-region Blu-Ray player, the BDP-S5500. Never had a day's trouble with it; everything worked fine.

Until today.

Long story short, it's locked on Region A and I can't change regions. I changed from B to A about a month ago and everything was fine and I've changed many times over the years with no issue. And now all of a sudden, pressing the blue button for region b does nothing (nor does the red for region c). I've tried a factory reset, checked to see if the firmware was up to date, and everything seems fine (I've made sure quick launch is turned off). I've also had a look around online and nobody else seems to have had this problem.

Any help would be immensely appreciated.

Thanks