Gradle/IntelliJ: Locking up lib files
There may be a java.nio.file.FileSystemException thrown on running the command after switching versions in preprocessor_branch.
Current tempfix: Either restart your IDE (as your IDE is locking up a file) or use tools like LockHunter to unlock the linked file. (Often a lib file under common\build\lib or forge\build\lib or fabric\build\lib).
Current believe is that the IntelliJ is reading the generated lib file with read/write instead of read. But for why is currently unknown.