This is odd, this came up once before with Vista (which I think was hacked fake RTM version). What version of windows are you using, and what .net framework and sp? PS: GameExtender viewer normally gives a black screen if it cant connect. EDIT: It is odd because a cast from "5.2" to a double is in fact valid, this should not be an error. I would try uninstalling .net 1.1 completely and try .net 2.0 or ensure you have the service pack for 1.1