This issue may appear as the result of various situations.
First of all, you must be sure that no 3rd party software are activated in your computer and carry out a virus scan.
Cheats previously used and belonging to different games can be used for Zula as well so these 3rd party programs are detected by the system as cheats even if they were downloaded and started only one time.
Since such kind of files can damage the functioning system of Zula, even if one user is able to log-in they will be kicked from the game right away.
This issue can also be experienced due to optimization works.