Hi Gary!!!
When I have an this type of error, I "hack" the class Library and fix the problem.
It sounds like the class does not know where to get the reference to the cbotypes object.
Try the following:
First thing make a back up of your class libraries. Then Try this:

** Try this with the copy
** First use the class library that holds the form 
** you are dealing with.
close data all
Use YourClassLibrary.vcx in 0

** then you can look for the objects within the classed form that has the cbotypes problem.
browse for upper(alltrim(parent)) = 'YourConvertedScxFormThatIsNowA_Class'; 
       and Upper(alltrim(baseclass)) = 'COMBOBOX' ;
       and upper(alltrim(objname)) = 'CBOTYPES'


** If you have a combobox named cboTypes this will take you to it.
** Now you have to look at the following:
**   1) Look at the Class field....Make sure it is the right name you want
**   2) Look at the Classloc Field.... Make sure it is pointed to the right classlib

**After you have made the changes need to get everything pointed in the right direction, you can:
Close data all
Compile Classlib YourClassLibary.vcx

After the compile There should be a different result.
HTH