Table &: (Switching not allowed)

What causes this issue?

For performance reasons, synchronous maintenance of matchcodes from the
database interface of the SAP System is subject to certain
restrictions which the system checks when update type 'S' is selected
for a matchcode ID. For example, only a directly dependent secondary
table may be used in a matchcode ID for the primary table that is to be
maintained synchronously. A directly dependent secondary table is one
where a foreign key relationship, in which the primary table is defined
as check table for the secondary table, was selected in the matchcode
object definition between the primary and secondary tables.
If you interpret the tables and the relationships between these tables
in the matchcode object definition as simple graphs, the tables being
the nodes and the relationships the links, then no branches may occur
in the parts of the graph determined by the matchcode ID tables.
Text tables, i.e. tables which are linked to the primary table by means
of a text relationship, are an exception to these restrictions.
These tables can always be included in the matchcode ID
even if this means that the matchcode ID contains more than one
directly dependent table.
<LS>Example</>:
( "A <- B" means a foreign key relationship from B to A, i.e. A is
check table for B)

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

A <- B, A <- C is not allowed if B and C are not text tables for
primary table A, since this would mean that two non-text tables (B and
C) are directly dependent on A.
A <- B, B <- C is allowed as only B is directly dependent on A,
and C is only indirectly dependent via B.
A <- B, A <- T is allowed if T is a text table for A, since in this
case only B, the only non-text table, is directly dependent on A.

System Response

The system checks the restrictions described here and issues an
appropriate error message.

How to fix this error?

Include only those matchcode object tables in the matchcode ID which
do not violate the restrictions or check your relationship definitions.

Error message extract from SAP system. Copyright SAP SE.