How to resolve VS2010 Windows Form Designer issue (base class could not be loaded)

I had the same issue. I had a Form object/base object I was inheriting from, and all of a sudden I see this message for all Forms that were inheriting from the Base.

I tried to backtrack and figure out what changed recently and remembered I set my project Platform Target from Any CPU to x64. I changed it back to Any CPU and the problem got resolved, and then setting it back again to x64 still kept the problem fixed.

This was on VS 2013, by the way.

I would suggest putting your base class in a separate project. As you obviously know, the problem is that VS is losing track of some meta information, which you can get it to find by quitting and rebuilding. If the base class is in a separate project, a clean/rebuild is more likely to bring it back up to date.

I've been having this issue a lot recently and found an easy and fast workaround and decided to share it (works for me on VS 2012).

When you have a Form like this:

public partial class MyForm : MyBaseForm

and the designer fails to design MyBaseForm saying the base class 'System.object' cannot be designed, all I have to do is to remove : MyBaseForm and revert (Backspace > Ctrl + Z). The designer will come to its senses then.

public partial class MyForm : MyBaseForm // The designer has trouble with this
public partial class MyForm              // Force an error
public partial class MyForm : MyBaseForm // Revert back, the designer should now work again

All that's left to do now, is to wait for Microsoft to fix that annoying bug.