原来出错的代码如下：
<p style="margin-top:0;">
<asp:TextBox ID="txtContent" runat="server" TextMode="MultiLine" Height="450" Width="98%"></asp:TextBox>
</p>
出错的原因应该是IE7、IE8中的P不支持innerHTML。CodeMirror的作者也发现了这个问题，相关链接：
https://github.com/marijnh/CodeMirror2/issues/215 https://github.com/marijnh/CodeMirror2/commit/4886415d6054571f92fa4d5601ebe7d601e952ab
try { stringWidth("x"); }
catch (e) {
if (e.message.match(/runtime/i) || e.message.match(/运行时/i) )
e = new Error("A CodeMirror inside a P-style element does not work in Internet Explorer. (innerHTML bug)");
throw e;
}
把textarea外层的p改成div，即可正常：
<div style="margin-top:0;">
<asp:TextBox ID="txtContent" runat="server" TextMode="MultiLine" Height="450" Width="98%"></asp:TextBox>
</div>
