The cause of Java compile error most of the time is that you added a appstore module and there are conflicting Jar files. Double check your userlib and check if you have multiple versions of the same Jar. Most of the time you can solve it by keeping the latest version and removing the other(s). But that is not always the sollution. This blog post gives good insight in the problem and what to do if the problem persists: https://www.mansystems.com/blog/mendix/managing-java-dependencies-for-mendix-modules

Regards,

Ronald