This number of key fields is not permitted with generic buffering

What causes this issue?

You want to buffer a table generically but have specified an incorrect
number of key fields. For generic buffering you need to specify a
number of key fields between 1 and n-1, where n represents the number
of the key fields of the table. If the table has only one key field,
generic buffering is not possible.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

You can find out the possible number of key fields via the possible
entries help in the corresponding field. There select one of the
numbers specified.

Error message extract from SAP system. Copyright SAP SE.