Solid Element Operation not working

[tonyfitz]

I have been working on a project and have it nearly complete, now the Solid element operation trimming upwards on the existing terrain by the new driveway doesn't work.  I have tried everything that generally causes these sort of issues including running the operation numerous times again and no luck.  THe operation has been fine for the past 4 months and has only now just stopped working.  I have checked the layer assignment numbers to ensure they are different, checked Design options, renovation filters and MVOs that might interfere and no response.  Any ideas ?

[Lingwisyer]

How is the terrain and driveway modelled? Are there any existing SEO utilising these two elements?

Ling.

[tonyfitz]

They are both mesh objects, the driveway mesh has another SEO working on it and then the final driveway is extracted with upwards from the site mesh.  It has been fine for 4 months and only now just stopped working.