Glen,
Which version of Eclipse are you working with? Is the PHP extension installed? Please go to Help > CodeMix Extensions and check if the extension is installed. If you are working with latest version of Eclipse and Java higher versions, then please check these FAQs to fix the problem with extensions : https://www.genuitec.com/forums/topic/codemix-and-angular-ide-compatibility-issues-in-eclipse-2020-09/
https://www.genuitec.com/forums/topic/codemix-and-angular-ide-installation-issue-in-eclipse-2021-12/
If you are still seeing issues, then please share the Eclipse version details and .log file located at workspace dir/.metadata/.log (rename the extension to .txt and attach it here) to help us investigate futher.
Please note that CodeMix has already reached its end of life and no new releases or fixes will be made. See here for further details and MyEclipse 2021 as alternative.
–Swapna
Genuitec Support