I presume you have read KBase Article ID:463766 at support.businessobjects.com which advises to add the following trace command.
To resolve the behavior, add -crpetrace 7 and -trace to the command line parameters for the Crystal Reports Job Server, which handles scheduled reports, or the Crystal Reports Page Server, which handles on-demand reports, in order to enable advanced tracing.
Let us know what it shows. Beware though, tracing slows down processing and creates large log files.