look up cache files

[anuragvijay]

I have a question regarding the cache files created by lookup transformation. The informatica documentation indicates that the powercenter server creates two files with extensions .dat and .idx. however i noticed that there is another file created with extension .lck. We are using persistant cache files which are used by multiple sessions. Sometimes when multiple sessions are running, one or more sessions fail with a system error indicating that a shared lock could not be placed on the .lck file. But on other occasions sessions run smoothly when running simulatneoulsy. Can anyone point out why this is happening?
Thanks