profile_fields.tpl in 1.3.5 sp4

Has anyone encountered this problem:

I can’t modify anything in profile_fields.tpl and save it? Every time I do, I get only a partial screen displayed. I then restore it from the initial download and everything is OK, then I pull the module in and make no changes and save it and…once again, only a partial screen is displayed. It is like you can’t save this module after the initial upload. I have modified approximately forty other modules and this is the only one I am having problems with.

Any suggestions?