Cannot start mp "Class not registered"

[mrgnome]

TV-Server Version: ?
MediaPortal Version: 1.0 RC2
MediaPortal Skin: Default
Windows Version: XP pro
CPU Type: Core 2 duo
HDD: 250g sata
Memory: 2gig ddr2
Motherboard: gigabyte
Video Card: radeon 3850
Video Card Driver: catalyst 8.6
Sound Card: Internal Intel

I cannot start mp due to the following error, as soon as i click ok after the config screen:


System.InvalidOperationException: Unable to generate a temporary class (result=1).
error CS0007: Unexpected common language runtime initialization error -- 'Class not registered '

at System.Xml.Serialization.Compiler.Compile(Assembly parent, String ns, XmlSerializerCompilerParameters xmlParameters, Evidence evidence)
at System.Xml.Serialization.TempAssembly.GenerateAsse mbly(XmlMapping[] xmlMappings, Type[] types, String defaultNamespace, Evidence evidence, XmlSerializerCompilerParameters parameters, Assembly assembly, Hashtable assemblies)
at System.Xml.Serialization.TempAssembly..ctor(XmlMap ping[] xmlMappings, Type[] types, String defaultNamespace, String location, Evidence evidence)
at System.Xml.Serialization.XmlSerializer.GenerateTem pAssembly(XmlMapping xmlMapping, Type type, String defaultNamespace)
at System.Xml.Serialization.XmlSerializer..ctor(Type type, String defaultNamespace)
at System.Xml.Serialization.XmlSerializer..ctor(Type type)
at MediaPortal.Player.DSP.Settings.SaveSettings()
at MediaPortal.Configuration.Sections.MusicDSP.SaveSe ttings()
at MediaPortal.Configuration.SettingsForm.SaveSection Settings(TreeNode currentNode)
at MediaPortal.Configuration.SettingsForm.SaveAllSett ings()
at MediaPortal.Configuration.SettingsForm.applyButton _Click(Object sender, EventArgs e)
at MediaPortal.Configuration.SettingsForm.okButton_Cl ick(Object sender, EventArgs e)
at System.Windows.Forms.Control.OnClick(EventArgs e)
at System.Windows.Forms.Button.OnClick(EventArgs e)
at System.Windows.Forms.Button.OnMouseUp(MouseEventAr gs mevent)
at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
at System.Windows.Forms.Control.WndProc(Message& m)
at System.Windows.Forms.ButtonBase.WndProc(Message& m)
at System.Windows.Forms.Button.WndProc(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.O nMessage(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.W ndProc(Message& m)
at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)


I have tried reinstalling.
What can this be?