You've got commas instead of full-stops in the dB settings 
Umm … that is normal in European mainland countries, and because
locale=nl (Goedemiddag, Vincent!

) I expect that Vincent's Windows Regional Settings (Nederlands?

) specify
, as the decimal separator and
. as the 'thousands' separator—the exact opposite of the standard for USA and UK. So to sum up, Charlie, that is a red herring.

The non-appearance of the 'Preparing file …' dialog is more puzzling, because here, that dialog appears for
every file dragged from Windows Explorer (or a mAirList Browser Directory pane) and dropped on to the Playlist! It doesn't matter whether or not the file has previously been tagged with cue points: the dialog is (ik
denk) informing you that mAirList is
trying to load the corresponding MMD file, so the dialog should
always be displayed when a file is added to a Playlist.
Vincent: have you tried this with build 486 installed, which is the mAirList.exe currently in the Snapshot download directory?
[later] Oops! Looks like you
have tried this.

I admit I'm stumped by this one.

--
BFN
CAD