Hi Cathal,
finally I update my application with the previous version of Client API, (the only available with source).

Now, occasionally, I found the error reported below in the Log Events; may be is Client API related and, perhaps, the fix is in the new version, (I found many threads about this error).

I hope you can help me.

Regards 

Fausto

ActiveTabName: News
RawURL: /news.aspx
AbsoluteURL: /Default.aspx
AbsoluteURLReferrer:
UserAgent: Mozilla/4.0 (compatible; Synapse)
DefaultDataProvider: DotNetNuke.Data.SqlDataProvider, DotNetNuke.SqlDataProvider
ExceptionGUID: 458938ce-53f5-444c-9d0e-7b3845dcd8fa
InnerException: Exception has been thrown by the target of an invocation.
FileName:
FileLineNumber: 0
FileColumnNumber: 0
Method: System.Web.Script.Serialization.JavaScriptObjectDeserializer.DeserializePrimitiveObject
StackTrace:
Message: 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.RegisterControlMethods(Control CallbackControl, String FriendlyID)at ArcadiaWeb.Framework.AJAX.AjaxPortalModuleBase.Page_Init(Object sender, EventArgs e)at System.EventHandler.Invoke(Object sender, EventArgs e)at System.Web.UI.Control.OnInit(EventArgs e)at System.Web.UI.UserControl.OnInit(EventArgs e)at System.Web.UI.Control.InitRecursive(Control namingContainer)at System.Web.UI.Control.AddedControl(Control control, Int32 index)at System.Web.UI.ControlCollection.Add(Control child)at DotNetNuke.UI.Modules.ModuleHost.InjectModuleContent(Control content)at DotNetNuke.UI.Modules.ModuleHost.CreateChildControls()at System.Web.UI.Control.EnsureChildControls()at DotNetNuke.UI.Modules.ModuleHost.get_ModuleControl()at DotNetNuke.UI.Containers.Container.get_ModuleControl()at DotNetNuke.UI.Containers.Container.ProcessModule()at DotNetNuke.UI.Skins.Pane.InjectModule(ModuleInfo objModule)
Source: