Attached is a document that explains the basic functionality of Contentdownload(CIC) and how to troubleshoot and problems you might have.
If the documents does not help resolve your issue, you can always create a support issue, just make sure to upload the following:
ca\sc\cic\conf - config.xml
ca\sc\cic\logs - All the logs files, if there are too many delete them all, and rerun cocntentdownload task 1 more time, then upload the logs.