Plugin Installation missing in iManager

Hello,

I need to install additional iManager Plugins. At the iManager configuration page there is only 'Role based services' and 'iManager Server' but without 'configure iManager'. All others, especially 'Plugin-Installation' is missing. iManager says (in Details), the signed-up user is not authorized to manage iManager, but I don't believe it. I've found many references to configiman.properties, I entered AllUsers or AllUsers=true, but it did not solve the problem. Also admin is in configiman.properties in correct syntax. So i don't think that it is the problem.
Strange thing: we have 6 Servers in the tree (one Netware 6.5, the others are OES2 till OES11.1) and all iManagers show the same behavior! So i think it is not a problem of the local iManager of one server, maybe a problem of the tree(?).
For browsing i use IE8, also tried Firefox, its the same. Client OS is Windows7 and WinXP.

Does anyone have suggestions to solve the problem? Or is there a manual way to install plugins? (I need the IDM plugins).

Regards

E.Gruber