TeamCity webserver hangs intermittently

We're using the NAnt runner on our builds, and now the TeamCity web app is intermittently locking up.  It doesn't seem to be using excessive heap or CPU resources, but gradually more and more threads end up waiting on the build log.  When we restart the server, it shows up as a failed build that timed out waiting for the build log:

java.lang.RuntimeException: Timeout while loading build log, buildId = 115 at jetbrains.buildServer.serverSide.buildLog.BuildLogImpl.waitForBuildLog2Load(BuildLogImpl.java:32) at jetbrains.buildServer.serverSide.buildLog.BuildLogImpl.loadMessagesIfNeeded(BuildLogImpl.java:62) at jetbrains.buildServer.serverSide.buildLog.BuildLogImpl.getMessagesState(BuildLogImpl.java:152) at jetbrains.buildServer.serverSide.buildLog.BuildLogImpl.getLastBlockMessage(BuildLogImpl.java:114) at jetbrains.buildServer.serverSide.stat.AntMessagesProcessor.openBlock(AntMessagesProcessor.java:149) at jetbrains.buildServer.serverSide.stat.AntMessagesProcessor.access$2100(AntMessagesProcessor.java:36) at jetbrains.buildServer.serverSide.stat.AntMessagesProcessor$BuildBlockProcessor.processBlockStart(AntMessagesProcessor.java:5) at jetbrains.buildServer.serverSide.stat.AntMessagesProcessor$BlockStartProcessor.processBlockStart(AntMessagesProcessor.java:2) at jetbrains.buildServer.serverSide.stat.AntMessagesProcessor$BlockStartProcessor.processMessage(AntMessagesProcessor.java:10) at jetbrains.buildServer.serverSide.stat.AntMessagesProcessor.doProcessMessage(AntMessagesProcessor.java:41) at jetbrains.buildServer.serverSide.stat.StatisticsMessageProcessor.processMessage(StatisticsMessageProcessor.java:22) at jetbrains.buildServer.serverSide.impl.RunningBuildImpl.processMessage(RunningBuildImpl.java:58) at jetbrains.buildServer.serverSide.impl.RunningBuildImpl.addBuildMessage(RunningBuildImpl.java:437) at jetbrains.buildServer.serverSide.impl.RunningBuildImpl.initBuildLog(RunningBuildImpl.java:290) at jetbrains.buildServer.serverSide.impl.BuildStarter$1.run(BuildStarter.java:1) at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:417) at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:269) at java.util.concurrent.FutureTask.run(FutureTask.java:123) at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:650) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:675) at java.lang.Thread.run(Thread.java:595)