The cause of the problem is that in the class you want to open in VFP6 you have defined in VFP5 a property that is now in the standard lenguage. Let's say, if in Custom class you have created a Tag property because it didn't exist. But now in the new version exist already, VFP6 doesn't know what to do so it won't open.
The solution is very easy, edit you class in VFP5, remove all properties that are now reserved, then open it in VFP6.
If it works send me a dollar!

>>>>>>I have a class created in VFP5 that I am trying to open in VFP6. I get a "syntax error" whenever I try to open any of the classes based on forms. Does anyone have any ideas ?