obj file won,t merge right with other sops and the model turn black then the node say A mis-match of attributes on the inputs was detected. Do I have to use convert op or save the geometry as different format so this will work. Everything else merge fine, but this obj file.

It probably has normals on it. Just slap down an attribute sop and delete N from the points. If that doesn't work MMB on each thing you are mergeing and check what attributes are present on each one, any that aren't the same will be set to 0 by default in the merged vesion. You can open up a spreadsheet to see this.

is it a maya obj model? The normals are probably reversed. Try a Reverse SOP.

no XSI.

One of the inputs to the Merge SOP has point normals. Either destroy the point normals before or after the merge with a Point SOP or add point normals to all the geometry again either before or after the Merge SOP with either a Point SOP or Facet SOP.

The problem is that the Merge SOP does not build point normals based on the surface primitives. If one of the inputs has normals, the other geometry will get normals initialized to 0,0,0 and subsequently shade to black.

I believe that many obj exporters create point normals so I would not be surprised if XSI did this.

Unless it was critical to keep the point normals from XSI, I would simply blow them away ( I do all the time). I would also turn on primitive normals and check to see that they point outward. If not, then use a Reverse SOP and reverse the primitives.