Dropdown list is not supported in view clusters.

What causes this issue?

A dropdown list display format is used in the current maintenance
dialog (view cluster &V1&, subdialog &V2&) for a field for which the
screen flow logic contains a <LS>PROCESS ON VALUE-REQUEST</> statement.
Dropdown lists cannot be automatically supported for this field.

System Response

The field cannot be displayed as a list box, so no possible entries
help is possible.

How to fix this error?

If this is an SAP table maintenance dialog, contact SAP.
If it is your own view cluster, you can:
Set the Screen Painter element attribute <LS>Dropdown</> to space for
all fields for which the module VCL_HELP_VALUES is called in the flow
logic. The field is then displayed as a normal input/output field with
standard F4 help.
If you really want to display the field as a list box, replace the POV
module <LS>VCL_HELP_VALUES</> in the underlying screen with a module of
your own based on VCL_HELP_VALUES. Call the function module
<LS>VIEWCLUSTER_HELP_VALUES_NEW</> in your module. Enter &V2& as
parameter <LS>OBJECT</> and the name of the field for which the help
module was called as parameter <LS>FIELDNAME</>. Your module need not
contain any more statements.

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.