Filezilla Server, FTP client issues

I'm running Filezilla Server on a custom built box, I have set all my users up and their passwords. I set their permissions to have correct permissions to modify, create, delete, append, and create directories and delete directoris.

My users use filezilla client as well as Windows Explorer to do transfers to and from the server.

My problems are. when i first create user accounts i and my users can cut/move and delete but after 30-40 minutes or so or after making a few transfers with the ability to cut/delete through windows explorer the ability is lost with an error that pops up stating "Invalid Handle" .

On the Client Side we use Windows explorer more so than file zilla client (file zilla will always allow us to delete), but my question is why do i loose the ability on my clients to move and delete though the settings state the same as i set where, i have set them . Can anyone shed some light onto as why i lose this ability.

Please help with this


Thanks,
Jon

theres no specific time frame, it will work when set for a little while, then later on it refuses to move the files from the server directory that the user cut and placed on their own pc. When i open up filezilla server interface and check their permissions and either make changes or uncheck and recheck settings their able to move and cut and later on the problem occurs again, i need to find a fix for this as we have 15 users accessing the same documents and files and cant have 2 or more users working the same files.