Hi @KING, Heather
At run time, the report processor checks whether the report definition (.rdl file) conforms to the schema specified in the namespace declaration at the beginning of the .rdl file. If a problem is detected, "The definition of the report <report name> is invalid" will be reported.
You can refer to this link: https://askgarth.com/blog/how-to-fix-the-ssrs-error-definition-of-this-report-is-not-valid/.
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