What causes this issue?

In the formula area, you can only select objects in the <ZH>technical
view</> by double-clicking.

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?

Switch to the technical view.
To do so, on the maintenance screen of the expression, in the
<ZK>Formula</> section, choose @BB@ <ZK>Technical/Long Text</>.
Double-click to select the required object.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.