I'd say the primary cause of this is points defined on a CAD split line - fairly common with cylindrical parts which have be generated with a Revolve type operation - if you do as Singularity said, moving points by 0.001" or 0.001mm will usually sort it, or in the case of cylindrical parts simply Transform and rotate the model 1°.
The other times I see this is where a scan is doubling back on itself (and ends near where it starts) and you move the start point the other side of the end point, so it does actually generate but stops immediately.
I'd say the primary cause of this is points defined on a CAD split line - fairly common with cylindrical parts which have be generated with a Revolve type operation - if you do as Singularity said, moving points by 0.001" or 0.001mm will usually sort it, or in the case of cylindrical parts simply Transform and rotate the model 1°.
The other times I see this is where a scan is doubling back on itself (and ends near where it starts) and you move the start point the other side of the end point, so it does actually generate but stops immediately.
