Excel 2007 : Date calculation incorrect!

[Schibbinger]

Hey guys.
My Excel 2007 seems to be too stupid to calculate dates correctly.
I want to use the Workday function to calculate and end date.
However, when i enter the formula "=WORKDAY(U4, 1)" Excel adds about 4 years and 1 or 2 (random) days.
Since i do not understand why Excel does so, i checked the function arguments. These are :
Start_date: 39213
Days: 1
=40676

WTF?
Any1 an idea?

[Bob Phillips]

Hard to say, it works properly and it works here so it is something in your environment.

Can you post the workbook?

[Schibbinger]

Not atm.
I never read about any1 who experienced that kind of prob either. Its so stupid!