I can't keep my POP access enabled.

I can't keep my POP access enabled.

When I change it from disabled to enabled, I get a confirmation in the bottom right hand corner that the changes have been saved, but when I leave, and then go back into settings, it's back to being disabled. I just bought my first iPad, and I can't send and receive e-mails through my zoho account, unless I enable the access. How do I do this?