>It may be that the printer is setup for receiving ascii text characters, but Windows is sending graphics stuff. If that's the case, you'll need to set the printer up in graphics mode. Sometimes there's a dipswitch setting in the hardware which can accomplish this. For more flexibility, there is generally a control sequence (and ESC (char (27)) and then another character) used to switch modes. These can be sent to the printer with the ??? command.

DM printers are always set for text, it's the responsibility of the software to send an escape sequence to initiate graphic mode for the commands that follow. Now these commands may be very long, and if anything is incorrect, the printer will return to its default text mode. The possible errors may include (as Sergey pointed out) someone switching it off because of the paper jam, cable error, or even the spooler eating few bytes off the beginning of the spooled job. And this is not just dot matrix specific, it's all the printers - you can get this sort of GIGO stack (garbage in, garbage out) in laser and bubble jet as well. I've seen a lot of sheets of paper with just a @ printed on them, in Courrier 10, normal, black.
As for a sure fire way to make the labels text mode, aside from printing using single, double and/or triple question marks, if there's a version of FPD, it's very simple to create a label there, save it and run directly from VFP (no editing, therefore no conversion, use it as it is saved in DOS version). VFP will gladly run it, and there would be no problems with VFP's rendering a proportional-font-style .frx into a text only printout; this would be text-only all the way.

BTW, I've seen such a Mannesmann printer, it was standing on a steel table, and as it printed, the table was swaying an inch left and right. Some people said they saw the building move as well. It would print a box full of A3 paper (2000 sheets) in about four hours. The same goes for the equivalent Epson. The reason for existence of such printers are not only companies which have to print out thousands of bills each month, but also relatively small companies where the accountants want to have detailed history of each item on stock when the year is closed. When our local dairy factory wanted to print that (and imagine just yogurt being sent to about 200 places a day), we listened to the new big Epson whole day.