contact appear offline

Hi,
My friends and I are running the same version of Windows messenger Ver. 5.0,
and when we have our computers on, it show me as being offline to them, and
they are shown as offline to me, we all are using Win XP. It does show some
of my contact as being on line, and we can chat bac-n-fouth with IM, but I
don't understand why it shows 3 of my friends as being off line, when I know
that they are on line. I use remote assistance quite often to help out my
friends, and right now I have 3 friends who need a little help, but I can't
help them because messenger is showing them as offline. Could really use some
help on this one, it got me stumped, also there are no firewalls turned on.
Does anyone one know how we can fix this?

Thanks Eml