When opening a drawing that is from someone else, they may have set the drawing to plot/print using a “Style” that has a file extension of “.stb” instead of a “.ctb”
What is a “.stb”?
The settings that define how a drawing looks when it is printed can be defined by either how it handles each color in the drawing (.ctb = Color Dependent Plot Style) or by wrapping up many of the various plot settings as a “Style” (.stb = Named Plot Style).
When you come across a drawing that has plot styles (,stb) and not your usual .ctb files simply use the command CONVERTPSTYLES <enter>
It will notify that it will no longer be looking for .ctb files
Just to verify that it worked, look in the command line…
Now the drawing should be able to see your .ctb files when plotting.