Hello all,

I'm following a book by sitepoint called 'Build your own ASP.NET 4 website' and I've come across a problem. I created a database diagram but when I save it I get the following message and I'm not sure how to fix it. Can anyone shed some light please as I have gone over the chapter in the book to make sure I haven't missed out something but everything seems to be right. I just can't seem to figure it out.
thank you.

Code:
'HelpDeskStatus' table saved successfully
'HelpDeskSubjects' table saved successfully
'HelpDeskCategories' table saved successfully
'Departments' table saved successfully
'Employees' table
- Unable to create relationship 'FK_Employees_Departments'.  
The ALTER TABLE statement conflicted with the FOREIGN KEY constraint "FK_Employees_Departments". The conflict occurred in database "HelpDesk", table "dbo.Departments", column 'DepartmentID'.