What layout are you on when the script runs? What table is it based on?
Refers to two different Tutorial: What are Table Occurrences?: Client_Activity_SCHEME and Client_SCHEME
One, the other or both are apparently not accessible from the context of your current layout. This will be controlled by:
1) What table occurrence is selected in Layout Setup | Show Records From for the current layout
2) What relationships link that table occurrence to other table occurrences in your relationship graph, such as the two referenced in your set field step.
3) the values in any match fields of the current record on your layout.
A common mistake here is that a developer will set up a script to create a new record and then can't see why a subsequent set field step fails to modify a field, not realizing that a new record may have empty match fields and thus not have any links to records in related tables from which to reference one or the other table occurrences in the set field step.
Thanks for your reply.
After reading your reply, and running it again, I noted on the script debugger am getting an error 103, so it does indeed look like the relationship is missing/incorrect. I will investigate further, but appreciate your reply.