Instrument tracks & settings changing randomly between sessions

Hello,

We are using Logic 9 at our school for all music tech course work and have recently been encountering a problem where all instrument tracks have changed from their assigned instrument to another random instrument, along with all of their settings too.

This happens between lessons; so when the project is saved and then re-opened a couple of days later, the instruments have changed.

We are running on OS 10.6.8 across a network.

So far we are putting it down to possible network issues but in most acses the students are using the same iMacs each time and there are no warning windows refering to lost path ways or files.

Any help, tips or advice would be very much appreciated.