FTP server config - user blocked

I need some help trying to figure out this issue: When a user tries to connect to an FTP they are placed on a firewall block right after trying to connect or perform upload/download. I was using the following FTP server configuration: TLS Encryption Support: Required (command) TLS Cipher Suite: HIGH:!aNULL:!eNULL:!PSK:!RC4:!MD5:!aDH:!DH:!SSLv3:!TLSv1 Allow Anonymous Logins: No Allow Anonymous uploads: No Max Load for anonymous downloads: 4 Max idle time: 15 Max connections: 50 Max connections per IP: 8 Allow logins with root pass: No Broken clients compatibility: No I have switched it to: TLS: Encryption Support: Optional TLS Cipher suite: HIGH:MEDIUM:+TLSv1:!SSLv2:+SSLv3 Anyone has any idea as to what could have been causing it? Was it TLS Encryption support? Thanks in advance!