I had this error today when trying to launch a .net application on a remote host machine. The file io exception threw me somewhat as it made me think that the issue was with loading a config file.
In fact the culprit of this error was not the config files, it was in fact missing dlls that are normally referenced from the GAC.
As I had no idea which dll it didn't know about, I just set each dlls reference to say copy to local = true, and then deployed the whole contents.
