Hi Mohammed,
Do you really need a parameter in the Subreport, if its being filtered based on a database field?
Try this:
1) Right-click the Subreport > Change Subreport Links > Remove all the links to the subreport
2) Get inside the Subreport and remove the record selection formula.
3) Delete any existing parameters
4) Go back to the Main Report > Change Subreport Links > Move the formula field to the pane on the right > Check the option 'Select data in Subreport based on field' > Choose the {engine.rptno} field from the drop-down
This will automatically filter the records in the Subreport based on the value from the formula being sent into the Subreport.
-Abhilash