You have included one or more Subreports in your main report, selected Preview, selected your parameters and then encounter the error “Error: Subreport could not be shown” before the report renders. This is seldom a good sign, however with an understanding of the common causes and a planned approach can be easily fixed.
The following thread explains there could be a number causes that can be contributing to this error.
Basically, you need to run your Subreport independently and make sure the subreport is working. If there is a problem within the dataset for the Subreport, you will encounter this error when previewing from the main report.
Once this is proved to work independently, but is still not working when previewed from the main report, work your way up checking parameter properties for multi select and nullability are the same between main and Subreports. This is a good reference for specifying parameters for subreports Parameters for Subreports.
If still no luck, then check the numerous other items discussed in the threads above.
If you are now rocking in the corner of the room from the experience, and are now asking yourself “Why do I even need a Subreport?”, consider the pro’s and con’s of Subreports discussed here Mark Hudson Considers Subreports.
Happy Subreporting !