I installed Dymo's label printing software. I fired up a test PC with a fresh load of Windows 10 Pro 64 bit. Apologies for the long post.Possible idea, the addon is 32-bit and Office is 64 bit? However the software, once installed, seems to work well enough. Seems to me that this company has terrible documentation which leads to a terrible experience. I restored my “DYMO Label Software” folder to my Documents folder as that is where my custom labels are stored. The Dymo 400 was there I didn't even need to “Add” it it was already there.

On a hunch (or last gasp), I restarted the machine and suddenly everything worked. I still had no luck with the Add Printer Preference Pane and the Dymo Label app. I then installed v8.4.2.9 with the Dymo unplugged and plugged it in only at the end as recommended. By the way, the Dymo uninstaller is a joke. Using EasyFind, I removed all Files containing the string “Dymo” in them except for the cups Dymo 400 Labelwriter.PPD and a cups filter “rastertodymo.” I had to enable EasyFind to look for hidden files and folders and iTweax to make hidden files appear in the Finder. Also, the Dymo Label app could not find the printer and advised reinstallation. Main problem was that the installer would run satisfactorily, then in the OS X Printers and Scanners Preference Pane, I would try to Add (+) my Dymo 400 printer and the Name and Location of the printer were shown, but the driver could not be found. I managed to get v8.4.2.9 working on my MBP Core 2 Duo running Mountain Lion and connected via USB. If this happens, you can either turn off drop shadows or switch the display to either 256 colors or millions of colors and the distortion will not occur. With some video cards set to display thousands of colors, you may notice that label shadows are distorted or have the wrong colors.

Printers connected to a serial port or using a Serial-to-USB adapter are NOT supported.

The LabelWriter 300, 330, and 330 Turbo printers mentioned in the list above are only supported when connected through a USB port on your Mac computer. DYMO Labelwriter for the dedicated Dymo label and tape maker machines, supports the following printer models:

Dymo 64 bit drivers