The provided information is not sufficient to identify what exactly is causing "Object reference not set to an instance of an object" error in the report.
How do you use the parameter - for filtering on the data source level, or on the report item level (Table), or in some other way? Generally, the report parameters are available/accessible all over the report, so there should be no problem when using them in multiple report items/components.
If you would like us to try to give you specific advises, please, open a support ticket and send us the problematic report so we can test it locally.
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