The line item dimension &1 is already assigned to characteristic &2

What causes this issue?

The selected dimension was defined as a "Line Item Dimension", meaning
a dimension that should contain exactly one characteristic (for
example, document number).
This is a special case for the dimension definition whereby a pointer
is not written to a dimension table in the fact table of the InfoCube
(as usual), but rather directly to the (SID) value of the
characteristic.
Several characteristics should now be assigned to the selected
dimension. This is not possible; a line item dimension can only include
exactly one characteristic.

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?

Decide which characteristic should be assigned to the "line item
dimension" and assign all other characteristics to other dimensions or
define the dimension as a normal dimension.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.