MP3 Plugin in Sound Forge Audio Studio 14 is not working, What could it be?

This is a common complaint, search 'MP3' in this forum as well as in the Vegas Pro audio forum. Usually reinstalling Sound Forge will rectify the issue. Uninstalling SF prior, is usually not necessary. If it condition persists, uninstall again using a third-party uninstaller (Revo for instance) which can clean left over data the default uninstall leaves behind.

btw, welcome to the Magix Sound Forge users forum @Edson-Sobrinho