خطای A potentially dangerous Request.Form

[rezaei manesh]

سلام
من یک freetext box در صفحه دارم وقتی که یه متن رو می نویسم و تایید می کنم درست کار می کنه اما اگه هر عملی رو توسط منوهای freetext box روی متن انجام بدم مثلا رنگ رو تغییر بدم حتی اگه دستی هم تو کد ها این کار رو انجام بدم خطای زیر رو می ده
دلیلش رو نمی دونم ؟؟؟

 A potentially dangerous Request.Form value was detected from the client (ctl00_ContentPlaceHolder1_FreeTextBox1="<div align="center">...").

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.Form value was detected from the client (ctl00_ContentPlaceHolder1_FreeTextBox1="<div align="center">...").