Abantecart on Namecheap seems broken! I am still trying to sort out the latest issue (of many) with Namecheap.
I had a working V1.2.16 copy installed that seemed to be working fine until upgraded to v1.3.0 and then I noticed that I could no longer edit the email templates. Just hours ago I took the plunge and reinstalled v1.3.0 using Softaculous and the error when editing email templated happens in a brand new untouched copy of Abatecart, so it looks like Namecheap is at fault somehow. I'm about to try and sort it out with support but I'm considering a new host!
Didn't mean to hijack your thread, just thought some more info would help you.