KiXtart 4.5 as in:

4.50
4.51
4.52
4.53

Is it possible DB is open for lock by another account or user ?
If security is not set correctly so that each user has write access to the folder then they can't create their own locks to the DB.

Do you get any errors on screen ? If not then I'd start adding some error codes to the script so that you can see what and where it's getting to until it errors.