Problem

WARNING: Only n% of surfaces have been meshed!
Additional meshing may be required to display other views of this solution.

The file <(><<)>file name>.shp will be required for additional meshing.
Saved rendering database to <(><<)>path to design file>\<(><<)>name of file>.ptd

This message is appearing in Message Center when saving Particle Trace Solution to file.

Solution

Disable "Visible Surfaces Only".
This simply means that the current Particle Trace solution is not a complete rendering solution for the whole model.

This is caused by processing a solution while "Visible Surfaces Only" in the Particle Trace settings is enabled.

Steps to correct (if the need to render all surfaces is wanted):
1. Go to Settings > Rendering > Particle Trace
2. Go to the Meshing section.
3. Disable "Visible Surfaces Only".
4. Recalculate solution.