Hiro, so you are able to see CTB file in the list of avaliable plot style tables in Page Setup dialog, via Format -> Plot Style menu, in Properties Inspector, but when you open it you see the message "Error finding path"? And looks like AutoCAD cannot use this Plot Style table?
Are you able to use standard CTB files? I mean if you apply monochrome.ctb - does your plots became black and white instead of colored with acad.ctb?

Maxim