Hello Burnley81,
Likely both tasks occur during the same 4 hours. Project flags a
resource as overallocated not due to the number of hours h/she works
in a day, but due to the highest assignment (peak units) reached.
If you schedule two tasks each for 2 hours and assign the same
resource at 100% assignment units, the resource will show in red
(overallocated) even though the total amount of work on the day is
only 4 hours.
I suggest changing the date format through Tools > Options, View tab
to show date and time. I imagine you'll see the two 4 hour tasks
overlap in time.
Take a look at FAQ 34 "Overallocation Occurring In Les Than One Day"
at:
http://project.mvps.org/faqs.htm
I hope this helps. Let us know how you get along.
Julie
Project MVP
Visit
http://project.mvps.org/ for the FAQs and additional
information about Microsoft Project