I have been trying to upload a song to bandcamp, who insist on an uncompressed file at a minimum of 44.1kHz.
I checked in audacity/preferences that that’s what the sample rate was before I exported it as a wav file, but it won’t upload because bandcamp tell me the file is only 22.05. 
Why is this happening and how can I fix it?
Set the Project Rate (lower left corner of the main Audacity window) to 44100 before you export.
Export in WAV format.
Is there any requirement for mono/stereo?
Cheers! 
Actually, now you ask the question about mono/stereo, the L/R faders no longer seem to make any difference. Is theis because I’ve changed the sample rate?
I’m not sure exactly what you mean - the sample rate should not affect the functioning of the Left/Right track sliders.
Can you give me a step-by-step example of how I can reproduce this problem?
I appreciate they shouldn’t have anything to do with each other, it just seemed odd that it should happen just after I changed the sample rate…
Anyway, since I’ve restarted my computer they work again. Very odd. Thanks for the help again.