Crystal Reports: Subreports run independently but stall when running within report

I have a report that includes 11 subreports, all of which connect to the same set of tables. Each subreport runs fine when executed independently. When I refresh data on the main report, the data refresh stalls and will not move to the next subreport after the 6th one is completed (all records show and 100% shown in status bar). If I remove the 6th subreport , the report will refresh without incident. What is could be causing this single subreport to stall the data refresh?