The selected items can only be processed together

What causes this issue?

During the calculation of interest, there can be dependencies between
the various items of a form. For example, interest is only calculated
for invoice-related credits, if interest is also calculated for the
related invoice.

System Response

Therefore the system does not offer updating of interest for selected
items.
Instead, all items that belong to a form are now selected. If you
selected the items of multiple forms, then the items of multiple forms
are selected.

How to fix this error?

Start processing again.

Procedure for System Administrators

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

Error message extract from SAP system. Copyright SAP SE.