Drop Down Data Validation Menu Doesn't Work When Opened on Different Computer

Hi guys!

I'm brand new here, so please excuse any faux pas!

Ok, here's my situation:

Using Excel 2010, I set up a simple workbook with a spreadsheet on one page and the ranges for data validation on another.
I successfully linked the fields in the "Category" and "Tender" columns with the data on the second sheet, making nice drop down menus.
Everything works fine on my computer.
However, when we open the workbook on a different station, the drop down menus disappear. If you highlight any of the "Category" or "Tender" fields, the little drop down prompt is missing; they behave like regular, un-formatted fields. It appears that the data validation became un-linked.

We tried opening versions with certain fields locked (Mainly the Total, Breakdown, and Summary areas, but the fields with data validation were still editable), and also completely unlocked documents. Every time, the drop down lists were lost when opened on different stations.

I've attached the completely unlocked version for anyone who's interested in trying it out.

Am I missing something here? Forget to check a box or something? This seems way harder for me to figure out that it should be!
Or is this a bug that others have encountered?

Any advice would be greatly appreciated!