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?