把acad.exe.config文件修改为：
------------------------------------------------------------------------------------
<configuration>
<startup>
<!--We always use the latest version of the framework installed on the computer. If you
are having problems then explicitly specify .NET 2.0 by uncommenting the following line.
<supportedRuntime version="v2.0.50727"/>
-->
<supportedRuntime version="v2.0.50727" />
</startup>
</configuration>
.net开发CAD2008无法调试的解决方法
原文地址：http://www.cnblogs.com/chinaHunk/p/7455207.html