No values assigned to node

What causes this issue?

In a matrix, a combination of values on the axes is referred to
as a node. To create a node, you must either select a value
combination or enter one. If a node exists in the intersection
of two values, you can display the node data by double-clicking on
the node.
You see the current error message because the value combination on
which you clicked does not yet exist as a node.

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?

Error message extract from SAP system. Copyright SAP SE.