Cover art upload

Hi guys,

I'm reporting this issue because every time a upload a image a get this error, and i tried to upload again and get the same message, then a closed the browser and in the picard a lookup in browser and open the page again and after that the image is upload, but some times a have to do this again few times until it upload.

Can you whats going on with the server or it's on my side that a have to do something?

Thanks.