421 Please reconnect using TLS security mechanisms

[spiros]

I try to uninstall a mod and I get this.

Trying to enter my FTP info results in them not being accepted. (FTP login is disabled on the server, one can only login via SSH certificate).

[Aleksi "Lex" Kilpinen]

(FTP login is disabled on the server, one can only login via SSH certificate).

That would probably explain this. You may need to make the files writable manually.