问题
解决方法：
1.降低.Framework的版本
<!--修改前-->
<system.web>
<compilation debug="true" targetFramework="4.5" />
<httpRuntime targetFramework="4.5" /> <!—将其删除-->
</system.web>
<!--修改后-->
<system.web>
<compilation debug="true" targetFramework="4.0" />
</system.web>
2.webconfig修改或添加关于"ValidationSettings:UnobtrusiveValidationMode"的value值
<appSettings>
<add key=" aspnet:UseTaskFriendlySynchronizationContext" value="true" />
<add key="ValidationSettings:UnobtrusiveValidationMode" value="WebForms" />
</appSettings>
删除<add key="ValidationSettings:UnobtrusiveValidationMode" value="WebForms" />即可。
如果没有上面两句的话：在appSettings字节中添加
<add key="ValidationSettings:UnobtrusiveValidationMode" value="None" />