Unsupported Operation. A document processed by the JRC engine cannot be opened in the C++ stack.

This is an inner exception that you may encounter with Crystal Reports, now it sounds rather bad, but its really just a badly named error – don’t panic (just yet anyway)!

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Unsupported Operation. A document processed by the JRC engine cannot be opened in the C++ stack.
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More than likely it is caused because the reporting engine can’t load your report due to a spelling error in the report name or an incorrect path to the report file.

In my case the problem arose because the report was defined in a different project to where it was displayed, so I just added a post build step to one of the projects so that the report file (.rpt) was copied to the output bin directory on a successful build, and its all ok now!