Problem:

Stress Isometric does not create a drawing file, why? Reason #6.

The following appears when trying to create a Stress Isometric:

Is not a recognized file format

Notice that all files but DGN file are created:

Solution:

Reset Profile Preference using procedure here. 

Afterwards, open model and try to create a Stress Isometric.

See Also

Reasons why stress Isometric was blank or does not create a drawing file?

OPIM Stress Isometric Troubleshooting Guide

Bentley AutoPIPE