Thanks everybody, a few hours of investigation found stray lines which was spotted with Smustard Stray Lines Plug in. As you say TIG it was a tiny unfinished loop which was wrong, I removed them, closed the loop and bam! Many thanks to you all, I can see this forum is going to be useful, but I'll try not to ask too many dumb ass questions! I'm OK with Final Cut Pro,Cinema 4D, Motion etc, but have just bought Sketchup and I'm really enjoying doing some engineering models on it. Thanks Again.

Patrick