Data Validation - List option

Hello guys, I am new to this forum and I have reading some really helpful information and tips.

I have a workbook in which I have data validation in some cells (it has a drop down with a couple of options). After sharing the workbook with a collaborator, this functionality does not work anymore even when I re-do it (does not show drop down arrow, no options).

But I can creat the same functionality in a new work book with no problem. Now, when I move the a sheet from the new workbook with this functionality (working) into the workbook that I had shared, the sheet looses the functionality (does not show the dropdown arrow and does not show the list of options).

I am using office 2010 and I am not sure how to fix the work book. This workbook has a lot of sheets which are interconnected with formulas and will need to sometime to creat a new one.

Thanks for your help.