WebDeskPro problem

System

After a clean installation of TS552+SP4; there is a very strange problem:
I login as administrator (any role) and get the error message "An error has occured trying to obtain the todo list. The message returned by the server is: GetSciErrorString is unable to open a session." When I switch to the Workarea view the branch list is empty; the file list window contain the message "TeamSite Server: teamdev Version: 5.5.2 Build 23679 Interwoven 20030813" and virtually nothing seems to work. There is no "Create Branch" item in the menu for example.
TeamSite is working on the other hand; I can create branches using command line tools; I can access the task list using the Author Webdesk interface, etc.
TeamSite is running on W2KSP4, with all critical patches installed. What is going on?

Thanx.