What causes this issue?

You have attempted to carry out actions in a graphics window which
cannot be altered at present, because sub-windows are currently opened.

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

System Response

How to fix this error?

Carry out the action in the most recently opened window or close the
other graphic window first.

Error message extract from SAP system. Copyright SAP SE.