.ctb file missing from plot style table on particular drawing

[t.sutherland.design]

I have a .dwg drawing sent to me from a co-worker. Under Page Setup Manager, my custom .ctb file is not appearing under the Plot Style Table. In fact, none of the .ctb files that I have stored in the plot styles folder are not showing. The Plot Style Table Search Path is the same for this drawing as all other drawings. Any suggestions? 

[Patchy · Accepted solution]

Because it was converted to plot with stb so you have to convert it back.

[cadffm · Accepted solution]

The file is setup up for stb plotstyletables (named plotstyle)

Read more about convert plotstyles stb ctb

[t.sutherland.design]

This worked. Thank you.