It certainly sounds like a printer driver problem, but I wonder if it's possible that some weirdness is triggering font-space condensing. Since it doesn't show up in viewing your document, it's highly unlikely, but the same effect can be created by consensing font spacing by a large number.

After printing, is the doucment still OK as viewed, or has it taken on the overprint characteristics? If the latter, try clearing character formatting by selecting the text adn pressing Ctrl+spacebar.

Best,
Ulodesk