youtube plugin is not working

Message:
    java.lang.StringIndexOutOfBoundsException: String index out of range: -1
Level:
    SEVERE
Stack Trace:
String index out of range: -1
    java.lang.String.substring(Unknown Source)
    cz.vity.freerapid.plugins.services.youtube.YouTubeFileRunner.processConfig(Unknown Source)
    cz.vity.freerapid.plugins.services.youtube.YouTubeFileRunner.checkFmtParameter(Unknown Source)
    cz.vity.freerapid.plugins.services.youtube.YouTubeFileRunner.run(Unknown Source)
    cz.vity.freerapid.plugins.webclient.AbstractFileShareService.run(Unknown Source)
    cz.vity.freerapid.core.tasks.DownloadTask.doInBackground(Unknown Source)
    cz.vity.freerapid.core.tasks.DownloadTask.doInBackground(Unknown Source)
    org.jdesktop.swingworker.SwingWorker$1.call(Unknown Source)
    java.util.concurrent.FutureTask$Sync.innerRun(Unknown Source)
    java.util.concurrent.FutureTask.run(Unknown Source)
    org.jdesktop.swingworker.SwingWorker.run(Unknown Source)
    java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source)
    java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    java.lang.Thread.run(Unknown Source)