$decurlis already being modified by another WWWOFFLE server.
To ensure that only one WWWOFFLE server modifies each cached file at a time a lock file is used. While one server is modifying the cached file the lock file exists so that other servers know about this. Until the first server has finished the cached file is not valid and cannot be accessed by another server.
If you see this error message all of the time even when offline then it is possible that the lock file exists but there is no server modifying the page. This can only happen when the WWWOFFLE server that was modifying the page does not exit properly. It is important that you make sure that you allow the WWWOFFLE servers to finish and that you do not kill them or shut down the machine while they are still modifying a page. To remove the lock file it is necessary to purge the WWWOFFLE cache since this will clean up any bad lock files.