It happens when one task calls Close; but gets interrupted in the Close call, and another task then calls Open.
The call to Close, calls 'close' then later calls an FsNotify function to remove the closed file from the list.
When a task switch happens between these calls, the new task calls Open.
Open then calls 'open' and gets back the file handle from the previous call to 'close'.
Open then tries to call the FsNotify function to add the file handle to the list; but it is already there so it asserts.
OK, that makes sense (except the part where Canon didn't protect it with a semaphore or something...) Though it's surprising how reproducible it is with the autostart once script.
In all likelihood switching to always using 'open' in CHDK (even for writing files) would probably work and eliminate more instances of the problem - we don't use whatever the FsNotify code is doing.
It seems like this would be reasonable to try in the trunk for a while.
