Diagnosis
A foreign key which previously existed is deleted. This can have thefollowing reasons.
The key of the value table was changed structurally, i.e. the positionsand/or the number of key fields changed (type or length changes withoutchanging the position or the number of key fields do not cause foreignkeys to be deleted).
The value table was removed from the domain of the check field.
Another domain was entered for the data element of the check field.
The foreign key was purposely deleted from the ABAP/4 Dictionary.

Procedure
If the foreign key was automatically deleted and you do not want this,then you will have to create the foreign key again.
It might be necessary to adjust the field definitions of the dependenttable to the new value table.