[IronPython] Can't import System?

[Dan Eloff]

I created a winforms project in IronPython, compiled it and it worked
great. Then I made some changes and now it says it can't import any of
the .NET assemblies. FileNotFoundError: "Could not load file or
assembly 'System.Data' or one of its dependencies. The system cannot
find the file specified."

It happens for System, System.Data, System.Drawing,
System.Windows.Forms, and System.XML.

Does anybody have any ideas why this might be happening?

Thanks,
-Dan