[Baertram]

For the start I'd recommand logout.
As you can see this is a lam version included into LibGroupSocket. Try to delete the LibAddonMenu in the subfolder of this addon!
Then delete LibaddonMenu-2.0 from your live/AddOns folder and reinstall it fresh with the newest version into the live/AddOns folder.
Check ingame in the addon manager which version is enabled and make sure it IS the newest one and no older one coming from any other subfolder of any other addon.





P.S.
For your next error message posts:
Please click the checkbox at the bottom of the lua error message popup to show more detail and post the complete error message so we can see what additional details the error message provides (variable names e.g.). This helps a lot.
if you are using any addon which suppresses the error messages and you only get them into your notifications or chat: Disable this addons and let show the original error message in the popup, completely. Then copy & paste it from the popup including the details. Thanks.