>when the table have an autoincremental field.

Here's an excerpt from VFP8 Help:
Older versions of Visual FoxPro cannot recognize tables that use autoincrementing. If you remove autoincrementing, the current state containing the last incrementing and incremental values is cleared from the .dbf field subrecord and discarded. The .dbf type is restored to the current Visual FoxPro type value. The autoincrement values previously stored in each record remain.