brasero: "name.ext" is not suitable for audio or video media

I try to create an Audio CD using brasero 3.12.3-x86_64-1salix15 on a Slackware 15.0 based system. slapt-get added the following packages to meet all dependencies: The following NEW packages will be installed: graphene gstreamer gst-plugins-base libburn libisofs brasero The exact versions of the packages: 1/6 Get http://slackware.uk/salix/x86_64/slackware-15.0/ graphene 1.10.6-x86_64-1 [104.0kB]...Done 2/6 Get http://slackware.uk/salix/x86_64/slackware-15.0/ gstreamer 1.18.5-x86_64-1 [1.7MB]...Done 3/6 Get http://slackware.uk/salix/x86_64/slackware-15.0/ gst-plugins-base 1.18.5-x86_64-1 [2.2MB]...Done 4/6 Get http://slackware.uk/salix/x86_64/slackware-15.0/ libburn 1.5.4-x86_64-2 [288.0kB]...Done 5/6 Get http://slackware.uk/salix/x86_64/15.0/ libisofs 1.5.4-x86_64-1gv [259.0kB]...Done 6/6 Get http://slackware.uk/salix/x86_64/extra-15.0/ brasero 3.12.3-x86_64-1salix15.0 [2.4MB]...Done Starting brasero I get no errors in the terminal that started it: rava@rava1:/$ brasero When I click the "Audio project / Create a traditional audio CD" icon nothing happens in the terminal, but when I then click on the "+" icon ("Add files to the project") and the Open File Window opens, the starting terminal tells me this (brasero:8385): GLib-GObject-WARNING **: 20:31:29.706: attempting to add an interface (EggTreeMultiDragSource) to class (GtkFileSystemModel) after class_init The same error is repeated every time I go around in my filesystem (only the time stamp of the error changes) And when I select any .wav or .mp3 that should be suitable, I always get this error: "name.ext" could not be opened. "name.ext" is not suitable for audio or video media. **I tested several files that should be suitable, but all create the above error.** Since the file I want to burn as Audio CD is sampled as 48000 Hz I used lame to convert that into a 44100 Hz highest quality mp3 because when in audacity-linux-3.2.1-x86_64 I set the sample rate to 44100 Hz but the exported .wav file still had 48000 Hz. lame --resample 44100 --preset extreme lamesh_11100_1.wav This is what ffprobe reports on that mp3 that I converted via lame mp3 with the above parameters: $ ffprobe -hide_banner lamesh_11100_1.mp3 Input #0, mp3, from 'lamesh_11100_1.mp3': Duration: 01:03:39.49, start: 0.025057, bitrate: 216 kb/s Stream #0:0: Audio: mp3, 44100 Hz, stereo, fltp, 216 kb/s Metadata: encoder : LAME3.100 Side data: replaygain: track gain - 0.500000, track peak - unknown, album gain - unknown, album peak - unknown, but still, brasero keeps insisting on "lamesh_11100_1.mp3" could not be opened. "lamesh_11100_1.mp3" is not suitable for audio or video media. Any ideas why that might be? Is some dependency missing or not working correct and brasero not tells me about this?