The sequencer is run as part of a sql job. I checked with process explorer and the file is opened only by the sequencer. I just have to kill his process and everything returns to normal.
I have two job, one which run at midnight with full import and synchro. And another one, which runs each 15 minutes from 8am to 19pm on a delta basis. Sql job guarantee that the same job cannot run twice at the same time, and I have configured the sequencer to log to a different file for each job.
The fact is that after the sequencer step in full job, there is some steps that need to be run, to prepare the delta job.
Thanks for your feedback, I'll search around when it happens again.
Is there any more verbose mode on the sequencer ?