A project which has performed fine for many months started behaving badly today. I pressed the toolbar 'make' button after modifying a couple of source files. One core of the CPU was pegged at 100% with the status bar showing the background task "Clearing output directories". This continued for many minutes. I was able to close the project and shut down cleanly (confirming that I wanted to shut down even though background tasks were running). Restarting, loading the same project and attempting to make the project reported that the previous compilation hadn't completed and that a full rebuild was required. The process stuck again at Clearing output directories... Again, I could shut down cleanly. All output dirs were empty. I've deleted the the content of IDEA's system directory and deleted my .iws file (the only project file to have changed in days). On startup my project libs are scanned (as expected after deleting caches) but things stick at Clearing output directories... whenever I perform any compilation. Attached is a CPU snapshot. I deleted the system dir contents and .iws file, started IDEA, loaded my project, started the snapshot capture, started rebuilding the project, waited 3 minutes and stopped the snapshot capture. The problem seems to be project-specific - another project rebuilds correctly - but none of the .iml and .ipr files has changed in days and I specifically deleted the .iws file. IDEA log file attached (but it contains no exceptions).