If a builds starts while someone is in the process of delivering to the integration stream the build will immediately fail with an error like the one below.
I have noticed this occur several times over the course of the past week

09:20:59 [builder_RavenPlatMain_Cavium_Uboot] $ cleartool lsactivity -fmt '\"%[headline]p\" \"%[stream]p\" \"%u\" \"%[contrib_acts]p\" \n' deliver.rmeyer_RavenPlatMain_10.20101205.090923
09:21:00 "deliver rmeyer_RavenPlatMain_10 on 12/05/10 09:09:23." "RavenPlatMain_Int" "vobadm" "Tools-fixing_chassis_rpm_with_xe80_platform rebase.rmeyer_RavenPlatMain_10.20101205.074249"
09:21:00 [builder_RavenPlatMain_Cavium_Uboot] $ cleartool lsactivity -fmt '\"%[headline]p\" \"%[stream]p\" \"%u\" \n' Tools-fixing_chassis_rpm_with_xe80_platform
09:21:00 FATAL: null
09:21:00 "Tools-fixing chassis rpm with xe80 platform" "rmeyer_RavenPlatMain_10" "rmeyer"
09:21:00 java.lang.NullPointerException
09:21:00 at java.util.regex.Matcher.getTextLength(Unknown Source)
09:21:00 at java.util.regex.Matcher.reset(Unknown Source)
09:21:00 at java.util.regex.Matcher.<init>(Unknown Source)
09:21:00 at java.util.regex.Pattern.matcher(Unknown Source)
09:21:00 at hudson.plugins.clearcase.util.ClearToolFormatHandler.checkLine(ClearToolFormatHandler.java:69)
09:21:00 at hudson.plugins.clearcase.ucm.UcmHistoryAction.callLsActivity(UcmHistoryAction.java:130)
09:21:00 at hudson.plugins.clearcase.ucm.UcmHistoryAction.callLsActivity(UcmHistoryAction.java:148)
09:21:00 at hudson.plugins.clearcase.ucm.UcmHistoryAction.buildChangelog(UcmHistoryAction.java:113)
09:21:00 at hudson.plugins.clearcase.history.AbstractHistoryAction.getChanges(AbstractHistoryAction.java:83)
09:21:00 at hudson.plugins.clearcase.AbstractClearCaseScm.saveChangeLog(AbstractClearCaseScm.java:515)
09:21:00 at hudson.plugins.clearcase.AbstractClearCaseScm.checkout(AbstractClearCaseScm.java:490)
09:21:00 at hudson.model.AbstractProject.checkout(AbstractProject.java:1119)
09:21:00 at hudson.model.AbstractBuild$AbstractRunner.checkout(AbstractBuild.java:480)
09:21:00 at hudson.model.AbstractBuild$AbstractRunner.run(AbstractBuild.java:412)
09:21:00 at hudson.model.Run.run(Run.java:1325)
09:21:00 at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:46)
09:21:00 at hudson.model.ResourceController.execute(ResourceController.java:88)
09:21:00 at hudson.model.Executor.run(Executor.java:139)