How to pass a Report Parameter to dataSourceExpression?

Hi,

Wonder if anyone can help.

I have a Report Parameter value defined within my TestCase. I'm then trying to use this param with a <dataSourceExpression> within my TestCaseReport (which is then calling a SubReport).

The line I have is:
<dataSourceExpression>$P{ParamDataSinkToUse}</dataSourceExpression>

but this is throwing the error: "Error evaluating expression : Source text : $P{ParamDataSinkToUse}".

I can however successfully use the parameter within a <textFieldExpression> so the value is definitely been passed.

Any assistance would be appreciated.