Just to add something to what dickevans said:
Have you checked your system clock? Are the date, time and time zone correct? Is it possible it is losing time (say over the period of a week) and it is at that time it fails?
Just to add something to what dickevans said:
Have you checked your system clock? Are the date, time and time zone correct? Is it possible it is losing time (say over the period of a week) and it is at that time it fails?