Hi Michael,
I have attached a sample file.
A - Is the initial construction which is then translated to the solid B - no problem.
C - shows when the blend gap appears... you will see in the top view the only difference is that I have tapered the curve inwards, but by doing this you can no longer get the blends to meet up.
D - with this one i added some extra points to the curve and bingo it worked fine...
I'm guessing that blending is quite sensitive to the smoothness of the original line work that you draw.

All in all i've achieved what i wanted now and learnt quite a bit in the process, thank to all who have responded.

http://moi3d.com/forum/get_attachment.php?webtag=MOI&hash=6b0ece3447c8c0fbc9c0eb1d016d921b&filename=Test.3dm