JExpressInstaller subdirectory is empty or missing

Message
There must be a subdirectory in the JExpress installation directory called JExpressInstaller with class files for the com.denova packages. This subdirectory or its class files are missing.

 

Comments
The most common cause of the disappearance of the JExpressInstaller subdirectory or its class files is that another program, such as an IDE, erased them. This can happen if you configure an IDE to use the JExpressInstaller as its target build directory for your custom classes. Many IDEs erase all class files in their target directory which destroys the class files distributed by JExpress.

The solution is to change the IDE's target build directory or configure the IDE not to erase the class files before it recompiles your custom classes.