Unable to log in, returning player from years ago

hey guys im hoping someone can help me out with this, i used to play on this server A LOONNGG time ago, im trying to log in now and i get this message "io.netty.handler.codec.DecoderException: i: Non [a-z0-9/._-] character in path of location: legacyslkeepalive". i can not pass this message and get sent back to the server select screen, mu assumption is im somewhere thats been built over or somthing. im hoping that maybe i can get my account reset or something as id really like to play again. my in game name is MrBEEAANS