My ZM400 printer is not printing correctly. I have an 8x4 label and it will only print half of the document. The half that it prints, is the first half of the document but prints at the end of the label. EX. I have a label that says HELLO across the entire 8". When it prints, however, it only prints HEL and not on the first 4" of the label but on the second 4".

SOURCE: Zebra 105sl - printer does not print correct size

This can happen if you have the wrong dpi setup. For instance the 105sl can be either 203dpi or 300dpi. If your printhead is 300dpi and the label you create is expecting 203dpi, then you will see shrunken label. Your situation doesn't exactly sound like this is the case but it may be worth checking.

SOURCE: I can't print label from ZM400 PRINTER thru' serial port

There are a number of parameters for the serial port that have to match the pc. i would print out a config page from the printer via the menu, or power on with the cancel key held. then compare it with the settings on the pc. on the config page you should be looking for things like data bits, host control, parity etc.

SOURCE: Our Zebra 105se printer has started missing

Clean your platen roller. It's the white rubber roller (that turns and pulls your labels through your printer) located under your printhead. When this gets slick it causes your labels to slip while printing.
You should use rubbing alcohol to clean it. Your computer guys may also have some cleaning wipes in a foil packet that you can use.

SOURCE: Print continuously

I know late, but we just had the same issue and it seems the sensors on the outside and inside needed to be cleaned. once that happenned, labels are not printing out continuously.

SOURCE: zebra zm400 turn printed info 180 degrees

Yu can rotate the print orientation in the Z Designer printer driver, in the OPTIONS tag tick the 180Deg box