We don’t have clear answers for this problem. Make sure the controls referenced in the toolbox correspond to the right version ( it could be a mix up of assembly version). You can actually remove all Xceed controls from the toolbox, then add them again, making sure you choose the latest version of the dlls. Make sure the dlls found in the references of the Solution Explorer have the same version.
Imported from legacy forums. Posted by André (had 502 views)