on a fresh install.  from the install wizard i tried custom, typical, and auto.  i've even tried changing the language but downdown seems to auto-postback.  i get all the same error.

System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.ArgumentException: Invalid JSON primitive: . at System.Web.Script.Serialization.JavaScriptObjectDeserializer.DeserializePrimitiveObject() at System.Web.Script.Serialization.JavaScriptObjectDeserializer.DeserializeInternal(Int32 depth) at System.Web.Script.Serialization.JavaScriptObjectDeserializer.BasicDeserialize(String input, Int32 depthLimit, JavaScriptSerializer serializer) at System.Web.Script.Serialization.JavaScriptSerializer.Deserialize(JavaScriptSerializer serializer, String input, Type type, Int32 depthLimit) at System.Web.Script.Serialization.JavaScriptSerializer.Deserialize[T](String input) --- End of inner exception stack trace --- at System.RuntimeMethodHandle._InvokeMethodFast(Object target, Object[] arguments, SignatureStruct& sig, MethodAttributes methodAttributes, RuntimeTypeHandle typeOwner) at System.RuntimeMethodHandle.InvokeMethodFast(Object target, Object[] arguments, Signature sig, MethodAttributes methodAttributes, RuntimeTypeHandle typeOwner) at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture, Boolean skipVisibilityChecks) at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture) at DotNetNuke.UI.Utilities.Reflection.InvokeGenericMethod[T](Type Type, String MethodName, Object Target, Object[] Args) at DotNetNuke.UI.Utilities.MSAJAX.Deserialize[T](String Data) at DotNetNuke.UI.Utilities.ClientAPI.GetClientVariableList(Page objPage) at DotNetNuke.UI.Utilities.ClientAPI.RegisterClientVariable(Page objPage, String strVar, String strValue, Boolean blnOverwrite) at DotNetNuke.UI.Utilities.ClientAPI.RegisterClientReference(Page objPage, ClientNamespaceReferences eRef) at DotNetNuke.UI.Utilities.ClientAPI.RegisterClientReference(Page objPage, ClientNamespaceReferences eRef) at DotNetNuke.UI.Utilities.ClientAPI.GetCallbackEventReference(Control objControl, String strArgument, String strClientCallBack, String strContext, String srtClientErrorCallBack, String strClientStatusCallBack, String strPostChildrenOfId, CallBackTypeCode eCallbackType) at DotNetNuke.UI.Utilities.ClientAPI.GetCallbackEventReference(Control objControl, String strArgument, String strClientCallBack, String strContext, String srtClientErrorCallBack, String strClientStatusCallBack, String strPostChildrenOfId) at DotNetNuke.UI.Utilities.ClientAPI.GetCallbackEventReference(Control objControl, String strArgument, String strClientCallBack, String strContext, String srtClientErrorCallBack) at DotNetNuke.Services.Install.InstallWizard.Page_Load(Object sender, EventArgs e) at System.Web.UI.Control.OnLoad(EventArgs e) at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)

Curly Fro,
I am getting hte exact same error message on one of my virtual machines.  I'm still digging into what might be causing the error message, but thought I'd let you know that it is happening elsewhere.  I'll let you know if I find any more information on what is causing the problem and/or a possible fix.