方法一、瀏覽器設定成相容模式。

方法三、點選VS的工具選單--》庫程式包管理器--》程式包管理器控制檯（如果沒有“庫程式包管理器”的選單，就先點那個“擴充套件管理器”，安裝一個叫“NuGet程式包管理器”，然後就會有了。），點選後下面會出現一個連線PowerShell的控制檯，等控制檯載入完畢後輸入

              install-package App_BrowsersUpdate  回車

               等待安裝完成後，網站根目錄下面會出現一個App_BrowsersUpdate目錄。然後再訪問就不會出現“__doPostBack未定義”的錯誤提示了。

以上的方法三解決不了IE11

IE11的解決方法是（下面方法二選一）：

二、在上面方法三生成的App_Browsers\ie.browser新增以下文字，在頂部的<browsers>下面：

1. <browserid="IE11"parentID="Mozilla">
2.   <identification>
3.     <userAgentmatch="Trident\/7.0; rv:(?'version'(?'major'\d+)(\.(?'minor'\d+)?)(?'letters'\w*))(?'extra'[^)]*)"
   />
4.     <userAgentnonMatch="IEMobile"/>
5.   </identification>
6.   <capture>
7.     <userAgentmatch="Trident/(?'layoutVersion'\d+)"/>
8.   </capture>
9.   <capabilities>
10.     <capabilityname="browser"value="IE"/>
11.     <capabilityname="layoutEngine"value="Trident"/>
12.     <capability
    name="layoutEngineVersion"value="${layoutVersion}"/>
13.     <capabilityname="extra"value="${extra}"/>
14.     <capabilityname="isColor"value="true"/>
15.     <capabilityname="letters"value="${letters}"/>
16.     <capabilityname="majorversion"value="${major}"/>
17.     <capabilityname="minorversion"value="${minor}"/>
18.     <capabilityname="screenBitDepth"value="8"/>
19.     <capabilityname="type"value="IE${major}"/>
20.     <capabilityname="version"value="${version}"/>
21.   </capabilities>
22. </browser>
23. <!-- Mozilla/5.0 (Windows NT 6.3; Trident/7.0; rv:11,0) like Gecko -->
24. <browserid="IE110"parentID="IE11">
25.   <identification>
26.     <capabilityname="majorversion"match="11"/>
27.   </identification>
28.   <capabilities>
29.     <capabilityname="ecmascriptversion"value="3.0"/>
30.     <capabilityname="jscriptversion"value="5.6"/>
31.     <capabilityname="javascript"value="true"/>
32.     <capabilityname="javascriptversion"value="1.5"/>
33.     <capabilityname="msdomversion"value="${majorversion}.${minorversion}"/>
34.     <capabilityname="w3cdomversion"value="1.0"/>
35.     <capabilityname="ExchangeOmaSupported"value="true"/>
36.     <capabilityname="activexcontrols"value="true"/>
37.     <capabilityname="backgroundsounds"value="true"/>
38.     <capabilityname="cookies"value="true"/>
39.     <capabilityname="frames"value="true"/>
40.     <capabilityname="javaapplets"value="true"/>
41.     <capabilityname="supportsCallback"value="true"/>
42.     <capabilityname="supportsFileUpload"value="true"/>
43.     <capabilityname="supportsMultilineTextBoxDisplay"value="true"/>
44.     <capabilityname="supportsMaintainScrollPositionOnPostback"value="true"/>
45.     <capabilityname="supportsVCard"value="true"/>
46.     <capabilityname="supportsXmlHttp"value="true"/>
47.     <capabilityname="tables"value="true"/>
48.     <capabilityname="supportsAccessKeyAttribute"value="true"/>
49.     <capabilityname="tagwriter"value="System.Web.UI.HtmlTextWriter"/>
50.     <capabilityname="vbscript"value="true"/>
51.   </capabilities>
52. </browser>

  <browser id="IE11" parentID="Mozilla">
    <identification>
      <userAgent match="Trident\/7.0; rv:(?'version'(?'major'\d+)(\.(?'minor'\d+)?)(?'letters'\w*))(?'extra'[^)]*)" />
      <userAgent nonMatch="IEMobile" />
    </identification>
    <capture>
      <userAgent match="Trident/(?'layoutVersion'\d+)" />
    </capture>
    <capabilities>
      <capability name="browser"              value="IE" />
      <capability name="layoutEngine"         value="Trident" />
      <capability name="layoutEngineVersion"  value="${layoutVersion}" />
      <capability name="extra"                value="${extra}" />
      <capability name="isColor"              value="true" />
      <capability name="letters"              value="${letters}" />
      <capability name="majorversion"         value="${major}" />
      <capability name="minorversion"         value="${minor}" />
      <capability name="screenBitDepth"       value="8" />
      <capability name="type"                 value="IE${major}" />
      <capability name="version"              value="${version}" />
    </capabilities>
  </browser>
  <!-- Mozilla/5.0 (Windows NT 6.3; Trident/7.0; rv:11,0) like Gecko -->
  <browser id="IE110" parentID="IE11">
    <identification>
      <capability name="majorversion" match="11" />
    </identification>

    <capabilities>
      <capability name="ecmascriptversion"    value="3.0" />
      <capability name="jscriptversion"       value="5.6" />
      <capability name="javascript"           value="true" />
      <capability name="javascriptversion"    value="1.5" />
      <capability name="msdomversion"         value="${majorversion}.${minorversion}" />
      <capability name="w3cdomversion"        value="1.0" />
      <capability name="ExchangeOmaSupported" value="true" />
      <capability name="activexcontrols"      value="true" />
      <capability name="backgroundsounds"     value="true" />
      <capability name="cookies"              value="true" />
      <capability name="frames"               value="true" />
      <capability name="javaapplets"          value="true" />
      <capability name="supportsCallback"     value="true" />
      <capability name="supportsFileUpload"   value="true" />
      <capability name="supportsMultilineTextBoxDisplay" value="true" />
      <capability name="supportsMaintainScrollPositionOnPostback" value="true" />
      <capability name="supportsVCard"        value="true" />
      <capability name="supportsXmlHttp"      value="true" />
      <capability name="tables"               value="true" />
      <capability name="supportsAccessKeyAttribute"    value="true" />
      <capability name="tagwriter"            value="System.Web.UI.HtmlTextWriter" />
      <capability name="vbscript"             value="true" />
    </capabilities>
  </browser>