I've just installed the plugin for the first time (v 1.6.1.2835) and I'm getting the same error. Seems it's baaack.
After a fresh install, make sure the AutoUpdate has run to get the latest Site code (otherwise you only have what was released months ago).
I just updated Youtube with the latest signatures.
[09-09 03:59:05,238] [OVLatest ] [WARN ] Error getting latest videos from 'YouTube': Value cannot be null.
Parameter name: s
[09-09 11:36:49,299] [OVLatest ] [WARN ] Error getting latest videos from 'YouTube': Value cannot be null.
Parameter name: s
[09-09 11:37:52,787] [OnlineVideos] [WARN ] System.Runtime.InteropServices.COMException (0xFFFFFFEC): Exception from HRESULT: 0xFFFFFFEC
at System.Runtime.InteropServices.Marshal.ThrowExceptionForHRInternal(Int32 errorCode, IntPtr errorInfo)
at OnlineVideos.MediaPortal1.Player.OnlineVideosPlayer.BufferFile()
[09-09 11:37:52,925] [OnlineVideos] [WARN ] OnlineVideos.OnlineVideosException: NoDataAvailable
at OnlineVideos.MediaPortal1.Player.OnlineVideosPlayer.BufferFile()
at OnlineVideos.MediaPortal1.GUIOnlineVideos.<>c__DisplayClass80.<Play_Step4>b__7c()
at OnlineVideos.MediaPortal1.Gui2UtilConnector.<>c__DisplayClass5.<ExecuteInBackgroundAndCallback>b__2()
[09-09 11:38:20,144] [OnlineVideos] [WARN ] System.Runtime.InteropServices.COMException (0xFFFFFFEC): Exception from HRESULT: 0xFFFFFFEC
at System.Runtime.InteropServices.Marshal.ThrowExceptionForHRInternal(Int32 errorCode, IntPtr errorInfo)
at OnlineVideos.MediaPortal1.Player.OnlineVideosPlayer.BufferFile()
[09-09 11:38:20,309] [OnlineVideos] [WARN ] OnlineVideos.OnlineVideosException: NoDataAvailable
at OnlineVideos.MediaPortal1.Player.OnlineVideosPlayer.BufferFile()
at OnlineVideos.MediaPortal1.GUIOnlineVideos.<>c__DisplayClass80.<Play_Step4>b__7c()
at OnlineVideos.MediaPortal1.Gui2UtilConnector.<>c__DisplayClass5.<ExecuteInBackgroundAndCallback>b__2()
[09-09 11:43:03,254] [OnlineVideos] [WARN ] System.Runtime.InteropServices.COMException (0xFFFFFFEC): Exception from HRESULT: 0xFFFFFFEC
at System.Runtime.InteropServices.Marshal.ThrowExceptionForHRInternal(Int32 errorCode, IntPtr errorInfo)
at OnlineVideos.MediaPortal1.Player.OnlineVideosPlayer.BufferFile()
[09-09 11:43:03,396] [OnlineVideos] [WARN ] OnlineVideos.OnlineVideosException: NoDataAvailable
at OnlineVideos.MediaPortal1.Player.OnlineVideosPlayer.BufferFile()
at OnlineVideos.MediaPortal1.GUIOnlineVideos.<>c__DisplayClass80.<Play_Step4>b__7c()
at OnlineVideos.MediaPortal1.Gui2UtilConnector.<>c__DisplayClass5.<ExecuteInBackgroundAndCallback>b__2()