This is documented in the VFP 8 help file. There were some changes made in VFP 8 to make it more compatable with SQL standards. Look at SET ENGINEBEHAVIOR in help, and RTFM.

>Fox2x memo fields are union incompatible in VFP8. The following code works in VFP7 but generates an error in VFP8:
>
>Close Databases
>Set Safety Off
>Create Table Test (MemoFld m)
>Insert Into Test (MemoFld) Values ('Some Text')
>
>* This line works
>Select * From Test Union All Select * From Test
>
>Select Test
>Copy To Test2x Fox2x
>
>* This line generate a "Selects are not Union Compatible" error
>Select * From Test2x Union All Select * From Test2x