@Eric-Kwak This seems like a problem caused by the license activation for the MP3 decoder/encoder. It looks like it shouldn't appear anymore in the new version, so try to update. But if that doesn't work for you usually a reinstallation of Sound Forge was suggested in the past.
Yes, updating is best, but if it persits, then you can resolve it by clicking: File > Reset all preferences and cached data. After that, close the program and restart it, and all should be good to go! ;)
Please try this, if it persits: Open SF, go to File > Reset all preferences and cached data. After that, close the program and restart it, and all should be good to go! ;)