A potentially dangerous Request.Form value was detected from the client

.net 4.0之前版本

修改web.config文件: 
<configuration> 
<system.web> 
    <pages validateRequest="false" /> 
</system.web> 
</configuration>

.net 4.0版本

还需要添加
<configuration>
<system.web>
        <httpRuntime requestValidationMode="2.0">
</system.web> 
</configuration>

asp.net mvc

需要在对应的Controller Action上增加[ValidateInput(false)] 特性