You issue may be caused by an earlier event where your system has been interupted during the actual transaction.
E.g. a power failure or a gui initiated sync which has left the system unresponsive and a forced shutdown has been executed.
When such event occurs - the kernel hooks has not been executed correct - thus leaving your system in a dysfunctional haf-finished state.
Only a manual cleanup can remedy such state.
A write-up on how to best avoid such issues can be found at below link