编译proxy code 的时候遇到这个问题估计是路径环境变量的问题有人知道如何改吗？

error CS2001: Source file 'system.dll,' could not be found
error CS2001: Source file 'system.xml.dll,' could not be found
error CS2001: Source file 'system.web.services.dll,' could not be found
error CS2001: Source file 'system.data.dll' could not be found