Class & is not supported for FI-SL planning

What causes this issue?

You want to go to the maintenance of the FI-GL part. However, the
planning parameters are assigned to a class which does not allow you to
use them for FI-GL planning.

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?

Change the assignment of the planning parameters such that you can also
use the planning parameters in FI-GL planning, or
Create new planning parameters for General Ledger.

Error message extract from SAP system. Copyright SAP SE.