after a upgrade from zencart 1.3.9c to 1.5.4 and installation of idealcheckout plug in my existing clients can not log in.
The client list is stil intact in the admin panel but if i tried to log in as a client nothing happens. No errors and no log in. Page remain the same.
If a make a new client entry, the new client wil apear in the admin panel. But even with a new client registration i can not log in.

Does someone know where i can solve this problem?