Error occurred during initialization of boot layer java.lang.module. FindException: Module javafx.controls not found

I am trying to build the sample javaFX application in the Intellij 2018.3 IDE. I have installed the oracle JDK11, and downloaded openjfk11. I created a library linked to the javafx sdk and added the line --module-path=${PATH_TO_FX} --add-modules=javafx.controls,javafx.fxml to the VM options line. PATH_TO_FX is defined as an environment variable pointing to my javaFX folder.

I have searched through a number of postings on this site, including This solution to my exact error message. The odd thing I cannot figure out is, This solution works for me if there is no build directory. But if I have already built the project once, it then refuses to run and gives me the stated error. If I delete the build directory and try again, then the program runs correctly again.