This happened after submitting the CL outside of IDEA:
Change 3376830 unknown.
com.intellij.openapi.vcs.VcsException: Change 3376830 unknown.
at org.jetbrains.idea.perforce.perforce.PerfCommands.checkError(PerfCommands.java:1639)
at org.jetbrains.idea.perforce.perforce.PerfCommands.executeFileCommands(PerfCommands.java:240)
at org.jetbrains.idea.perforce.perforce.PerfCommands.p4reopenFiles(PerfCommands.java:227)
at org.jetbrains.idea.perforce.application.ChangeListSynchronizer$6.run(ChangeListSynchronizer.java:388)
at com.intellij.openapi.application.impl.ApplicationImpl.runReadAction(ApplicationImpl.java:340)
at org.jetbrains.idea.perforce.application.ChangeListSynchronizer.checkReopenChanges(ChangeListSynchronizer.java:385)
at org.jetbrains.idea.perforce.application.ChangeListSynchronizer.access$300(ChangeListSynchronizer.java:58)
at org.jetbrains.idea.perforce.application.ChangeListSynchronizer$2.run(ChangeListSynchronizer.java:268)
at com.intellij.openapi.application.impl.LaterInvocator$FlushQueue.run(LaterInvocator.java:7)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:461)
at com.intellij.ide.IdeEventQueue.b(IdeEventQueue.java:85)
at com.intellij.ide.IdeEventQueue.a(IdeEventQueue.java:108)
at com.intellij.ide.IdeEventQueue.dispatchEvent(IdeEventQueue.java:13)
at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:242)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:163)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:157)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:149)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:110)