[sims] "registration must be at least 1 character(s) long"

[Gongalong]

Hi folks,

 

Trying to add a photo to a staff record and it won't save. I spotted I'm getting an error at the bottom of the record saying "registration must be at least 1 character(s) long". But I can't spot any field called "registration".

 

Any ideas what field this is?

 

Thanks