I developed a Access application using VBA. Everytime I open Access up, I get the following:
It's a per-user option. Everyone would need to 'trust' your workbook.
In Excel, hit the menu button, and choose Excel Options. In that window, pick Trust Center, and then Trust Center Settings. In that window, choose Trusted Locations.
Once on that screen, you will probably want to check "Allow Trusted Locations on my network" and then click Add Location and add the network location of your workbook.