Problem getting sub report to link with main report

I have a report that contains a sub report that works correctly.

I have a second report that I want to use exactly the same sub report from the first report.

• I have copied the sub report and inserted it
• I have set the Sub Report Links to be exactly the same
• I have set the record selection formulas to be exactly the same
• The parameters are exactly the same
• I can run the sub report independently and get data back

When i run the main report the sub report is blank

I have added the parameter field to the sub report and the when I run the main report I can now see the parameter fields so it is passing data.

However when i add the field that the parameter should populate it is NULL

Im really stuck as to why.

I can send the reports over to someone by email if they want to take a look.