This error may be caused by having the Hide Tabs plugin package installed but it not being up-to-date; the following should help to resolve the issue:
Locate and Update the Hide Tabs plugin package.
Have affected user(s) logout of RDB.
Have affected user(s) log back in to RDB.
Should this not resolve the issue, or the Login Tabs plugin appears to not be installed, please raise a new online case and refer to the title of this article.