iManager 2.6 issue with Configure tasks

[SchoellU]

Hi together,
i have suddenly a very strange issue and this over night of all my W2k3-servers with iM 2.6 in the tree (8.7.3.8).
Under Configure -> Plug-in Installation i press the task 'Available Plug-in Moduls', page is loading with finished-status, but nothing happens, only an empty site without errors returns. All other tasks works fine, all Tomcat .jsp-files (...webapps\nps\portal\modules\fw\skins...) are available and apparently ok, no updates for iManager or eDir are done, rights are ok.
Anybody an idea?
Thanks in advance for help.
Uwe