After upgrading a project with an mp3 in the timeline the following error message can occur.
In Camtasia Studio 8 we did not properly read the duration of variable bitrate mp3 files. In most instances Camtasia Studio would think the mp3 files was shorter than they actually were. We have corrected this in Camtasia 9. However, this can cause problems when upgrading projects. To start with you'll get the error message above which means the mp3 file will not show up in the clip bin as available media. If you right click the missing media and locate the correct mp3 file you will get this message.
This means that in order to use the mp3 file you will need to redo any edits that were made to that mp3 file. This problem will only occur with variable bitrate mp3 files that were edited in a Camtasia Studio 8 project and then upgraded to Camtasia 9. Another workaround would be to produce the Camtasia Studio 8 project as MP4 and import that MP4 file into a new Camtasia 9 project.