I have the same issue that you are describing. There seems to (sometimes) be a conflict over the Task Execution History files here as well. We use an application for monitoring that we have developed ourselves, and it reads these files.
I am thinking that it somewhat must be bound to happen when reading these files regularly, as they are updated every time a task is reloaded.
Were you able to figure out anything else?
Sorry for the late reply for anyone who has been following the thread. I have been on holidays.
My team made a batch file to copy the log files we are pointing our Sytem Monitor to. We only load the System Monitor once a day so the copy is made just before the System Monitor runs on it's normal schedule. By doing this we are not running off the 'LIVE' log files and there haven't been as many failures since we have done this.
Hope this helps