This error means that a user, may be yourself, previously logged on JartexNetwork as "tomason102" which means that only the exact username (username is case sensitive) will be able to log onto JartexNetwork. If this is first your first time joining Jartex then you will have to use some other username cause this means that the username is already being used by someone.
If you are using a premium account, You could change your username on the Minecraft site. If you are using a cracked launcher, you may change your username to whatever you like.
If this isn't your first time joining and you have previously logged on as that username, Please change the name to exactly "tomason102" and attempt to join once more.
Its not a bug or a gameplay issue as its not a problem from Jartex Side, nothings here to be reported
Also its not a password reset problem so, no need for password reset request. If that account isnt your I suggest you delete that report if you can