unable to edit or delete property fields in GroupWise library

[Dedmunki]

I'm trying to make one of the exisiting property fields for a library required but it will not let me edit. I was going to delete it and re-add it with the proper changes but I can't delete it either. I have noticed that other property fields in the library can not be modified while others can. Has anyone else come accross this issue?
Does anyone one have a fix?

Thanks
Julian