lost all additional fields

I have hit a disaster - I have amended an additional field using the control panel (changed an SQL field from text entry to dropdown box and entered the relevant data). Whn I hit submit all additional fields vanished. The records all seem to be there still, and I can view the data in the DEBUG INFO: payment system actions table but it doesn't appear in the reports section, or import/export or view membership details section.

This is the content I added to the school name additional field after converting it to dropdown select box: link. It must be the cause of the problem as the issue started immediately after submitting the changes. I hope this helps, but I don't see any obvious problems with it. Could this be related to the issue here: link In other words, was the list too long? And is there any way to recover the additional fields?

Thanks for any help you can give.

Matthew