XF 1.4 Users unable to login; FTP throwing Error

[xIsabel38]

So users on my site, including myself are suddenly unable to login. There is no error code, the page simply refreshes as if nothing happens when you attempt to log in.

New registrations to the site get this error:
"The field 'f016e4db7cd8b8eb9f4bbd2adbcbe8c0' was not recognised."

Additionally, when I access the site via FTP, my FTP is throwing this error at me:

I have not installed any new add-ons nor have I changed any files. Any ideas on what the issue could be would be appreciated.

Due to the FTP error, I'm wondering if this is a server issue.

Edit:
New User Registration is giving a bunch of weird errors:

 

[Mike]

The registration error is generally related to a template being out of date. It could also be a file issue. I could check the file health check and confirm the issue on the default style with all add-ons disabled. It is also possible that something is going wrong with sessions which may be triggering that.

The FTP issue is actually something related to the certificate used for FTPS. If you're getting this popup unexpectedly, you may want to contact your host to confirm details (though it is likely fine).

 

[whynot]

(though it is likely fine).

...and will be enough to tick "Always trust certificate in future sessions."

 

[xIsabel38]

Thanks for the responses. I contacted the server host and they basically said they rebooted Memcache which apparently fixed the issue. Not sure what any of that means but it's all working now.