Excel 2010 Checkboxes not clickable when given to certain users

I created a spreadsheet to give to other users, and on certain user's machines, the checkboxes within the form work, but on other's, they do not. These users are on the same corporate team, so they should have the same version of Excel.

All the checkboxes are Form Controls, not ActiveX. Also, the sheet is locked when I send it, but I've followed steps reported here, and here to no avail. I also checked here, here, and here, but the delete exd files approach isn't a good one here, because the end-goal of this worksheet is to give this worksheet the our users so they can give it to their users.

Is there some setting in Excel that I'm missing or is there a setting on the checkboxes? It seems that they're not enabled when the user opens the form, even though they're set up as enabled when I send the form out, and some of the users don't have any problem using the form.