The problem is not to many the problem is the exact, rather high number.
Filesystem stores its directory info in one block. When the block gets full it creats a new block to store the info in, allocating the second block and setting the links take time, ah does not run during that time and gets shot by its timetrap.
I dont know if the number is eaven fixed, might be the blocksize and filenames along with partition size matters.
I post that solely to explain why recording the 257th film works while the 256th one shoots you out.
Also, like skuzzy mentioned it depends on filesystem and other stuff.
As a suggestion, can ah2 at start up check how many files and free space are in film directory and warn/take actions if it senses a problem, maybe the people that get kicked out count how many files was the problem so you can pop up a message "200 files in film viewer directory, clear em out or you will have trouble recording".