"The given key was not present in the dictionary."

[Vadnais]

I am a new user to FOMM and when trying to startup it says I have to uninstall mods. However, when I select yes I get this error message: " The given key was not present in the dictionary. The mod was not uninstalled." What am I missing? If this has been answered before I apologize but my search skills are failing me right now...