Probably an easy question for the experts.
How can I create a MsgBox that would pop up to inform a user that they are
trying to enter data that is not allowed under the current condition?

Example:

Col A: Col B: Col C:
Day of week Status that day Hours of Regular Pay

Mon 8/7 Regular 8
Tues 8/8 Regular 8
Wed 8/9 Sick <<<<This cell (call it C5)
Thur 8/10 Sick is where I have the
Fri 8/11 Sick question

If the user types 8 in cell C5 above, I would like a MsgBox to pop up
because an employee can't get 8 hours of regular pay on a day they were coded
as out sick (cell B5). So under this scenario, only cells C3-C4 could
contain 8, cells C5-C7 should remain blank.

Any Ideas?
Thanks!