Microsoft Office Interop Excel Dll Version 12.0.0.0

Microsoft Office Interop Excel Download
Assembly Load Trace: The following information can be helpful to determine why the assembly 'Microsoft.Office.Interop.Excel, Version=12.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c' could not be loaded. I got solution by changing Excel.dll version. I was using 15.0.0.0 and now I. > Windows > assembly > GAC > Microsoft.Office.Interop.Excel > 12.0.0.0_etc. Could not load file or assembly 'Microsoft.Office.Interop.Excel, Version=12.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c' or one of its dependenciesRSS.

I have a program that reads data from excel.
I use:
Imports Microsoft.Office.Interop
as well as a Reference from the 'COM' tab called 'Microsoft Excel 11.0 Object Library'
I built my program then copied the .exe from the binDebug folder to a location on my company's server. I then double clicked the .exe and it ran as I expected it would.
My boss then tried (from another computer) and he gets this error:
Could someone explain why it works for me and not him? I am new to references but I feel that the problem is there.