Movie Maker audio problems (0xC946002C and 0xC946001E)

Here's where the issue started: When I tried to save a video with quite a lot of sound effects in it, it caused the background music to contain a few glitches in the final video. I tried to fix this issue by saving only the sound effects into a movie and then converting the MP4 file to an MP3 file by simply changing the file extension. However, when I tried to implement this audio back into my project, Error 0xC946002C came up, because "The file might be corrupted or in a format that Movie Maker doesn't recognise". I even tried unchecking the "Prepare files for faster editing" and "Prepare files for better stability" checkboxes, like an answer to a separate question on this website said, but that brought up Error 0xC946001E with the same message. How could I fix this issue?