Usually, this is caused by one of the following:
1) A tournament logo, especially if it's a.gif file, rather than a .png or .jpg. Try going to Settings - Tournament and deleting your tournament logo, then see if the printout works.
2) Text in one of the "message" boxes with hidden formatting. This usually happens when you've pasted in content from an external source, such as a Word document - you may not be able to see the special formatting characters, but they break the printout creator. To fix, clear out all the content in your message boxes (such as messages to print on ballots, postings, or judge cards...), and then try the printout again. If it prints, try pasting your message info into Notepad/TextEdit first to clear all the formatting, and then copy/paste it back to Tabroom.
3) An entry or judge with a strange character in their name or entry code, especially an & - to fix, look through the list of Entries and Judges, and remove any special characters you find.