Parameters are not sent to Sub Report on Sorting SSRS 2008

I am working with SSRS 2008. I have one main report and a sub report( out of the main table). Both the reports are rendered correctly. But as soon as I sort any of the columns in my report (main or sub report) I get the following error "one or more parameters were not specified for the subreport" though all the parameters were passed.

I tried to Google this error and found some suggestions like for sub report parameters if there are "available values" defined then such kind of error may surface but I checked that this is not the case here.

Note: Both the reports main and sub report take the same parameters.

Please suggest.