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>
------------------------------------------------------------------------------------
便搞定了。