This is a known issue present in the latest version of Telerik Reporting. The current error message, although giving correct information for missing report parameter values, is not appropriate in the described situation. Instead the report parameter validation should be happening at an earlier stage of the report life cycle
and showing the appropriate error message.
The issue has been logged in our system for improvement and we are going to introduce a fix for it in a future version of the Reporting suite.
We apologize for any inconvenience that this issue may have caused you.
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