Unable to cast COM object of type error...

I got a run time error: Unable to cast COM object of type 'MicroStationDGN.ApplicationClass' to interface type 'MicroStationDGN._Application'...

The app was done for MicroStation 8 2004 in VB2008. It works fine for 3 machines but not the fourth one.

The Bentley MicroStation DGN 8.0 Object Library is referenced.

Imports MicroStationDGN
dim msApp As MicroStationDGN.Application

...

msApp = new MicroStationDGN.Application

msApp.ShowError("test") 'this is where the error occurred.

Please help.

Thanks,