This is due to having the wrong verion of the MP3.dll file installed into the MP3 folder. How to check which version of the MP3.dll file is installed:1) Mac hard drive > System Folder > DAE folder > Codecs folder > MP3 folder.2) Click just once on the MP3.dll file to highlight it. Click on the File menu > Get Info > General Information. 3) Verify the version of the MP3.dll file. 4) Leave the MP3 folder open on the hard drive. The correct version for Pro Tools LE 5.3.2 is MP3.dll v. 1.2.2. It is on the Pro Tools LE v.5.3.2. installer CD. Here's how to install it:1) Open the Pro Tools LE installer CD. 2) Click on the View Menu and select "as List", to view the contents of the installer CD as a list.3) Open the DAE folder > Codecs folder > MP3 folder. Drag the MP3.dll file from the CD into the MP3 folder on the hard drive. The MP3.dll file will copy over.4) Launch Pro Tools and Bounce to Disk as an MPEG-1 Layer 3 file. The parameters windows will look normal and you should be able to bounce without error.