The errormessage may also be:

The JVM found at .\jre is damaged. Please reinstall or define EXE4J_JAVA_HOME o point to an installed 64-bit  JDK or JRE.

If this error occurs when you try to start JDownloader, your Antivirustool has probably removed a file called deploy.jar that belongs to the java virtual machine used by JDownloader.

1. Open your JDownloader Installationdirectory.
2. Delete the Folder “jre”
3. Try to start JDownloader
4. If it does not work, Install the latest Java Version at www.java.com/download/