Ok, I was getting frustrated with this issue, so I started trying to fiddle with just about every setting and application out on our desktops. This is what worked for me&
I opened up the Microsoft Office Picture Manager application. From the menu I selected Tools, then File Types. On all the machines with the problem the check box for JPEG was not selected. I selected the box, then OK, and then closed the application.
I returned to the Access database application and surprisingly the .JPG files opened in the users set default application and in most cases this is not Microsoft Office Picture Manager. I do not understand why this would work, especially when the users set application is something totally different. I also do not how this setting would get changed in the first place. Interesting, but it does, and my problem is solved.
Thanks for your help.