I'm going to assume you're talking about failed reports in either BusinessObjects or Crystal Server.
You'll need to look at the audit reports that come with the system. They use an Audit universe that also is provided. In order for this to work, you have Auditing turned on for, at a minimum, all of the Job servers in the system. You do this in the Servers section of the CMC.
Using the auditing feature is the easiest way to do this because the data is stored in a readable format in a database. In the CMS, the data is stored in a proprietary binary format which can't be queried directly - it can only be queried through the Query Builder tool, which doesn't allow export or show the data in a user-friendly format, or in a program that uses the SDK.
-Dell