Error in formula class &1: &2

What causes this issue?

Formula class &v1& contains errors and therefore cannot be used for
billing with the time-of-use interface.
This error is a programming error in the formula class. The error
message for the formula class is: &v2&

System Response

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

INCLUDE ISU_VERARB OBJECT DOKU ID TX

How to fix this error?

Correct the formula class.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.