Could it be because I am on a mac?

The macro works if I use it on linked cells from sheets within the
same workbook. But when I link to another workbook, open or closed, it
still forces me to "find" the workbook for each cell.

In essence, the dependent worksheet has information linked from the
first sheet of the dependent workbook and information linked from a
source workbook. There's a whole lot of linking going on. The first
sheet is a schedule that is copied to all other worksheets in the book
and then each sheet has information linked from source workbooks
updated by other departments, hosted on a server.