HCL Sametime Forum : Embedded sametime client missing from sidebar

Hi,
i have several users with Notes 9.0.1 client where the embedded Sametime client is missing from the Sidebar.
The problem is NOT only that it is a "hidden" panel in the sidebar.
If i open the menu "View-Right Sidebar Panel" i can only see "Feeds, Day at a glance and Sametime Primary Contacts". The "SameTime Contacts" and "SameTime Meetings" are not there at all.
In the Preferences of the Notes-Client is the whole SameTime-Settings and i checked that the Sametime client was selected during installation. I can even login from the Preferences and the user appears as online for others.
But he cant see others himself because he misses the "SameTime Contacts" panel in the sidebar.
Anyone has seen this problem?
Do you know if there is a config file where the sidebar panels are defined?

This happens for several users who had their clients installed for several years. The previous installation was done without the Sametime-Client. I manually started the installation for them and edited it so that the Sametime-Client was added.
The whole installation went through without any errors.
(I even tried to remove the whole Notes-Client installation and reinstalled it again, with same result. !! i kept their Notes-Data directory)

An other fresh installation of the notes client has no problem.
(I cant do fresh installations for all the users. It will be on dozens machines.)

Thank you in advance.