SAP Message 88665 - Execution of 2 monetary declarations at same time is not allowed

Diagnosis
You try to execute two cash declarations at the same time.
The following documents are regarded as cash declarations:
P = periodical declaration
J = annual prepaid declaration
E = final annual declaration
U = partial year declaration

System Response
The declaration cannot be executed.

Procedure
Change the consecutive documents of the main document type of the
recycling partner, since at least one consecutive document is of
type P, J, E or U.