2 hours ago, Rich Thomas 4D Engineering said:

Check the Edge Tolerance when you next try to use the Solids From Surfaces command - in Metric the default should be 0.075mm but I've known the figure to default to the English value instead which is 0.005.

Yes this was it. I increased the tolerances and it worked. Their was two faces/surfaces that were causing the problem.  Fortunately it highlights them once doing this so I have corrected it.

Was a surface on top of another surface.

Thanks   it's much appreciated!

Yes it's quite a complex part bit to simplify it imagine a square box drawn up in cad with six surfaces.  When converting surfaces to solid it would just create a hollow box.. as i mentioned I need the part to be a full solid however I'm unsure how you do it? I understand other softwares have ways to do this but I struggling to find it in mastercam

Anyone know how to do this.  I have already used the 'surfaces to solid' option but I then added a hole through the part and found it was hollow?

I need it to be a full solid body, any ideas?