Lately Illustrator has been a real pain in the butt for me at work.  Usually after messing around with a setting I can fix my issue, but this one has been stumping me for a bit.  I wanted to know if anyone here has had the same issue, and if so, how did you fix it?

I am currently running the CS5 suite.  When I try to export to Tiff, I get these wonderful lines.  When I open up the AI file in Photoshop, I sometimes also get lines, but not in the same places when using the same files.  It only happens with Tiff files.  Right now to get around it, I have to export as a JPG, then reopen in Photoshop and save as a Tiff.  The Jpg files do not have any lines in them.

When I change the anti-aliasing from "type optimized" to "art optimized" or "none", the issue only gets worse.  This leads me to believe that it has something to do with those settings.

I have used my google-fu to see if there was anything online about this.  People said things about lines appearing, but it didn't sound like my situation.  I checked for updates, but my version of AI is up to date.  Some of the stuff I read online said that when AI is exporting, it breaks down its images into blocks, and then reassembles it.  Could it be that some of the information is just getting lost?

EDIT: This appears to only happen when I place a tiff artfile underneath.  I tried just drawing a black box on a layer underneath and then exporting, and no lines appear.  It doesn't matter what art is placed underneath though, the lines always appear in the same place.  It almost looks like the vector shape is dissappearing, allowing me to see the artwork underneath.  When I placed a predominantly purple piece of art underneath, the line turned purplish.

Any help would be GREATLY appreaciated!

Cheers guys.