There is no active interface selected !! Click 'Help' for more details.

What causes this issue?

You have deselected the active interface from the global Partner
Integration.

System Response

Please make sure this action is valid as it could have serious
consequences:
o,,If there is an active integration partner, any data communicated
between SAP and the partner will fail as the SAP system uses this flag
to determine wether or not to integrate any incoming or outgoing data.
o,,Under no circumstances should this flag be de-selected for the
purposes of maintaining SAP ownership data using the SAP transactions.
<ZH>If this is the case SAP does not accept responsibility for any
problems arising as a result of the de-activation.</>

How to fix this error?

Ensure that the de-activation of an interface is valid. If neccessary,
check with your system administrator. If the interface has been
de-activated in error, correct this immediately by re-selecting the
active flag and saving.

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.