Do you have a Save from coming into port just prior to the upgrade? Investigating your report, it is found that the gun name has a typo in it. If you have an S-18 boat, it happens going from the 4" to the 3" gun. If you have an S-42 boat, the same happens later when going from the 3" gun to the 5" gun - if you happen to still be in an S-Boat at that time. The 4" to 3" change should happen after August of 1942 though, not in February of 1943. How long has it been since you docked?
If you have a Save prior to docking, let us know, and we'll try to get you squared away.