No transaction change. Do not set the activity category

What causes this issue?

You can specify the activity category in the first data record of a
variable transaction only. If you enter an activity category, this
tells the transfer program that a new block of data records is being
used (new transaction).
You entered the activity category but no block change is taking place.

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?

Adjust the transfer data accordingly.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.