IDEA Coverage generation fails

Hi,
I have some build configs which have begun giving the error, "Failed  to generate coverage report, error: java.io.IOException: Error loading  source names map from file  '/home/teamcity/teamcity-agent-2/temp/buildTmp/idea8325712501704946718coverage/coverage.ism'" instead of producing the statistics.  I checked and the coverage.ic and coverage.ism files exist in the stated location, but I don't know anything beyond that.  Has anyone else seen this?  I've tried running a clean checkout, and I've made sure that the file system isn't out of space.  (Running a Java 1.6 Ant build on a 64-bit Linux server.)

Thanks!