The report server cannot process the report. The data source connection information has been deleted. (rsInvalidDataSourceReference)

When using reporting services in Sharepoint Integrated Mode, you may encounter the error. This is to the fact that the datasource link is somehow broken on the reports.
To solve this:
1. Go to the reports folder on Sharepoint (where all the reports are published)
2. Edit data source on each report and link the datasource back.

This should sort out the issue.