With SSRS 2008, SOME subreports get Error: Subreport could not be shown

Hi,

I have been reading many of the web posts regarding the Error:Subreport could not be shown message. But none seem to fit so far.

Having recently upgraded to SQL Server 2008 R2, I have encountered the following:

I have a Reporting Services .rdl that invokes a number of subreports. All of the subreports use the same shared data source. SOME of my subreports render fine, some receive the Error: Subreport can not be shown.

Everything looks fine when I run the report from Report Manager. I am not using Report Viewer. I am not running locally. I am calling the Render method of the Reporting Services web service. The render method succeeds, but the byte string output of render (PDF) shows the error message in place of some of the subreports.

Can anyone visualize what would make SOME of the subreports fail?

Thanks in advance.