Important error in file uploading

Server reported an error - Attempt to invoke virtual method ‘java.lang.String com.backendless.AuthKeys.getVersion()’ on a null object reference
When do you think this problem arises?
I’m trying to upload a file (sample.txt). I used your code which was simple. Still it gave me this error.

Please, try this small code snippet on your file:

public static void main(String[] args) {
Backendless.initApp("APP_ID", "ANDROID_SECRET_KEY", "VERSION");
File testFile = new File( "/path/to/your/file" );
Backendless.Files.upload(testFile, "myFiles", true);

Please, notify us about result.