Cuffdiff shows errors

1. Open the attached "cuffdiff.uwl".
2. Set the "Read Annotations" input file: attached "transcripts.gtf".
3. Set the "Read Assembly" input file: attached "test.bam" twice. (two times the same file!).
4. Set the correct output directory for the Cuffdiff element.
5. Runs the schema.
Expected: the log does not contain any errors.
Actual: it contains the errors "Not an object! Id: [Id: 0, Type: 0, Extra: ], type: 0".