Custom Control Error "not Marked As Serializable"

The problem is, having converted from VS 2002 to VS 2008 the designer can't seem to handle the custom controls on "my" (not original designer) app. Any time I try to copy, in particular, the custom derived comboBox control I get this error initially:

Type 'Corporate.Controls.data.comboBox+comboBoxDataSource+Item' in Assembly Corporate.Controls, ... is not marked as serializable.

I chased this error down, marking classes Serializable and private variables therein as NonSerialized when they caused a problem (which might or might not be the smartest way to attack this problem...) but I've hit a brick wall. The most base corporate derived ComboBox class is:

Namespace Corporate.Controls
Public Class comboBox
Inherits System.Windows.Forms.ComboBox
...
End Class

It's unrealistic to post all of the relevant code (I believe). The short of it is:

System.Windows.Forms.ComboBox <- Corporate.Controls.comboBox <- Corporate.Controls.data.comboBox

I just kept backtracking through the errors.At this point I can't set System.Windows.Forms.ComboBox to Serializable. I've tried marking the Inherits System.Windows.Forms.ComboBox clause with <NonSerialized()> and while that doesn't cause a build error it doesn't seem to fix the designer-generated error in the other libraries when I go to actually add, copy or even delete the control in WYSIWYG. And that is the only reference to System.Windows.Forms.ComboBox in that (or any other) corporate library.