I just run across this valuable article. It talks about how to debug Windows Forms Designer errors you get on the screen when something goes wrong and I am pretty sure you get them here and there. So, if the error message that appears on the screen is not informative enough to solve the problem, or you are just plain curious, you can debug entire VS IDE and find the reason for the error WFD is throwing at you.
BTW, debugging whole IDE has other benefits, such as finding problems in components at design time.
Have fun digging into VS IDE.