Dear Sir,
The issue mentioned in the description appears due to the absence of reference material for the particular TAC. Kindly request you to generate a SOLAR support ticket to check the issue.
If you have the content backup of reference material then please copy the reference material for the course and paste it on ERAImpFiles (located where the content folder is set).
For example, Paste the reference material backup on the E:\ERAImpFiles\dl\rc folder path.