What does this error mean
 

Error: Cannot change na-bocht-1-0.75 to interior because there is only one adjacent cell thread. Error Object: #f

It is returned while reading a mesh created in Gambit. It's a model of a pipeline. I created some interior faces for postprocessing purposes in Fluent. " Na bocht 1 0.75 " is the name of the interior face

thanks in advance

Re: What does this error mean
 

How about checking your "Na bocht 1 0.75" face if it is jointed well between two volumes?

And... I wonder if you created that face after meshing your system.

Re: What does this error mean
 

The way this geometry is build is. First I made several volumes which are later united to one volume. Then this volume is split up in partial volumes (real connected in Gambit) en after this, all the volumes are meshed. So the volumes should be connected well and the interior faces are situated through meshcells.

Re: What does this error mean
 

I don't know your geometric system exactly. However, as far as I know, after using an unite option in GAMBIT jointed face would disappear. So, usually when a domain is decomposed, a jointed face is created after using the "unite option".

Anyway, if you want some surfaces for postprocessing, I think, a surface generation in GAMBIT is not necessary.

In Fluent solver, there is a function to create planes for postprocessing.