Yes the DPI is no need for image on screen - hence the reason I did not think about it when exporting photos...as I normally just export for screen. Furthermore, this was one of the first times I did not use the native LR Book Building Module. (NO exporting required)
It was only after I resized a few photos to the full page size that I started to get the error
Aufloesung zu gering. (Resolution too minor...direct translation). At first I thought it was because I was upsizing the photos beyond the normal range....but then I thought more and realized my error.
I ended up going with Paul suggestion of 8.3 inches and 300 dpi. It was not actually too difficult to redo the photos - just drag and drop.
It was
www.posterxxl.de - if you are interested. First time using them.