While developing in the Visual Studio for .Net you can get an error like this: "Interop type 'CrystalDecisions.Enterprise.SessionMgr' cannot be embedded. Use the applicable interface instead." or in German: "Interop Typ 'CrystalDecisions.Enterprise.SessionMgr' kann nicht eingebettet werden. Verwenden Sie stattdessen die anwendbare Schnittstelle."
To aviod this error, you have to change the properties of this reference. You have to switch the "Embed Interop Types" from True to False.
In the last time I had several problems with external access to a SAP BW System. The access was realized with an old version of the SAP Connector. And that is the problem. If you have a SAP Business Warehouse System version which is greater than 7.3, you maybe get troubles. For example SAP added new fields or like in 7.4 you now have the option for "Long text is XL" in the master data. So the old versions would not work with this.
I just found a very good table about the maintenance of all versions in Martins blog.