That "header" is probably not the header of a file maker layout, but data added to the beginning of the print job file spooled to your hard drive when you selected print.
Have there been any recent updates to your OS or printer driver?
Any changes made to your database about this time?
If you create a small test file with a labels layout and try to print from it, does it trigger the same error message?
If a test file doesn't trigger this message, try recreating your labels layout. (Do not copy any objects from your current layout).
If the new layout doesn't work, try recovering your file.
Things to keep in mind about Recover:
- Recover does not detect all problems
- Recover doesn't always fix all problems correctly
- Best Practice is to never put a recovered copy back into regular use or development. Instead, replace the damaged file with an undamaged back up copy if this is at all possible. You may have to save a clone of the back up copy and import all data from your recovered copy to get a working copy with the most up to date information possible.