This is an old question that still appears to have no answer, either here or in the wider forum pool, most advice relates to relentless clean>rebuilds or close>clean folders>reopen or restarting the machine. I don't have a solid answer at present though have done some research into it and thought I might share. Summarily, there is one location into which all designer files are copied when a control or form is designed, another location which old files can exist and a method is described to catch all designer exceptions before the designer can generate the error page.