You need a little more information to figure out the bug:
- Which server or build are you using?
- After what action does this window appear (for example, when entering, opening a menu, etc.)?
- Is there anything in the console or server logs at the time of the error?
The message itself shows that the client cannot find the required procedure (
Auth-ShowMenu) - most likely, the corresponding module/resource on the server is missing or incorrectly loaded. It’s hard to say more precisely without clarification, so if you send code or configuration information, it will be easier to help.