This problem is usually short-lived and transitory. Our recommendation is to refresh/retry. If that does not work then you should suspect your firewall or other network topology is interfering with the loading of all.js from Atlassian. Alternatively, it could be a problem with Atlassian's CDN for delivering all.js.
See the Atlassian task for ACJS-1134 - Investigate all.js CDN reliability
If the problem persists and your network administrator believes that local network issues are not preventing the loading of all.js then contact us via the Artemis Software Support Portal.