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 labelwriter 400 software for mac