Cubase 10 - Export to WMA file issue

Hi all,
First time poster here, so please go easy on me!
I’ve recently put together a composition, using around 10 instrument (midi) tracks, as well as a bass guitar (audio track).
The Cubase playback sounds fine. However, the problem is this:
As soon as I export to ‘audio mixdown’, and save the file as WMA (I’ve also tried WAV too), I playback the WMA file, and Windows Media player just won’t play the file back. I see from its properties that the WMA file does exist (it’s around 12MB in size).
I’ve tried to troubleshoot the problem: by ensuring the play locator markers are around the project and looking into the audio connection settings.
I’ve also just opened an old project I worked on and have successfully exported that to WMA, so that works perfectly. Therefore, it looks like I’ve inadvertently messed with some output settings?
Can anyone suggest what’s gone wrong here? I’m stuck!
Many thanks in advance.

It’s ok. Somehow it fixed itself. Phew.