Just to add in i have Gtk# 2.12 aswell.
The question remains: why do you have it? Clearly the problem is that the programs are trying to use Gtk# and not the version from the wiki. If you only have Gtk# because you were trying to get Basilisk II and Sheepshaver running, and you do not need Gtk# for any particular reason, then the easiest solution would probably be to uninstall it (from the Programs and Features control panel), and then re-install the version from the wiki.
If you do need to keep Gtk# for some reason, then you may have a problem getting the two versions to co-exist. GTK relies on environment variables and you may need to set up some sort of batch file to set the variables before launching Basilisk II or Sheepshaver, and then change them back after you finish running them.
Of course, if necessary you can just do without the GUIs and edit the configuration files manually.