"Unable to cast of type 'CrystalDec..."-error with Moss 2007 PIK and BO 3.1

I've deployed the new Portal Integration kit for Moss 2007 and BO XI 3.1 and get this error when I try to login:

"Unable to cast of type 'CrystalDecisions.Enterprise.InfoObject' to type 'BusinessObjects.Enterprise.Desktop.ClientActionSet'."

The error occurs when I try to login with the Content Explorer Web Part and being redirected to http://site_x/BOBJLogon.aspx

My server setup:

Server 1: BO XI 3.1 Server

Server 2: Portal Integration Kit 3.1 Build Version=12.1.5.989.Titan_iPoint_REL

BO XI 3.1 .NET SDK

MOSS 2007

Anyone having an idea?