Potentially dangerous Request.Cookies value w

Bonjour, je me suis connecté à vip.asus.com pour enregistrer un PC et voici le message qui apparait:
Description: Request Validation has detected a potentially dangerous client input value, and processing of the request has been aborted. This value may indicate an attempt to compromise the security of your application, such as a cross-site scripting attack. You can disable request validation by setting validateRequest=false in the Page directive or in the configuration section. However, it is strongly recommended that your application explicitly check all inputs in this case.

Exception Details: System.Web.HttpRequestValidationException: A potentially dangerous Request.Cookies value was detected from the client (fx="...g8SQ7v8KT3ONQ==").

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace:

[HttpRequestValidationException (0x80004005): A potentially dangerous Request.Cookies value was detected from the client (fx="...g8SQ7v8KT3ONQ==").]
System.Web.HttpRequest.ValidateString(String s, String valueName, String collectionName) +240
System.Web.HttpRequest.ValidateCookieCollection(HttpCookieCollection cc) +112
System.Web.HttpRequest.get_Cookies() +109
System.Web.HttpRequest.FillInParamsCollection() +57
System.Web.HttpRequest.get_Params() +132
member.login.Page_Load(Object sender, EventArgs e) +269
System.Web.UI.Control.OnLoad(EventArgs e) +67
System.Web.UI.Control.LoadRecursive() +35
System.Web.UI.Page.ProcessRequestMain() +2174
System.Web.UI.Page.ProcessRequest() +218
System.Web.UI.Page.ProcessRequest(HttpContext context) +18
System.Web.CallHandlerExecutionStep.System.Web.HttpApplication+IExecutionStep.Execute() +179
System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +87

Mes défenses: Avast et Malwarebytes'Anti-Malware. Aucun des deux ne détecte quoi que ce soit.
Que faire?
Merci