Error in Vcenter 5.5U1 Web Client and Plugin Update Manager

Hi

I upgraded my Vcenter Appliance from 5.5 to 5.5U1 without problems. And upgraded the Windows Update  Manager Server.

Now i have this error message when i open the Update Manager TAB in the Vsphere Web Client : "interface com.vmware.vim.binding.integrity.VcIntegrity is not visible from class loader"

It's works from the full Vsphere Client with the VUM Plugin.

What can i do ??

Thank's