if the wav/mp3 you are using to loop looks like the pic below then you have to do this
1. click the arrow that shows this menu and click split stereo track
2. should look like this now
3. then go on the menu for each track and select mono
4. should look like this now
5. once you export as ogg you will see this message
6. this is what it looks like when its saved, this will work in blockland
There is another way, which might be a little more faster.
After uploading your stereo song/loop file, go to 'Tracks' and go down three to 'Stereo to Mono', click it, then wait for the process to finish. Once it's done (assuming you've already made your loop), export it as a .ogg in the blockland music folder.
An example name: What_Ever.ogg
Will appear as: What Ever (in-game)
(Note: it's only grey colored because I did not have any song uploaded)
:D