I get it a few time on my Hostnoc hosting, it happens when you have something running at the back of your WordPress (i.e. cron job or schedule backup up etc), this happens when you put a lot of usage on the server. Make sure you save each and everything before pressing publish.
Furthermore, changed the values in cPanel, in the server, but you can do it in the php.ini file:
upload_max_filesize = 64M
post_max_size = 64M
max_execution_time = 300