看来我的一位同事编辑了 web.config 并添加了请求过滤，他删除了DEBUG"动词.这不允许在 F5 上进行调试.添加后(或删除请求过滤)一切正常.

It appears that one of my colleagues has edited the web.config and added request filtering where he has removed the "DEBUG" verb. This disallowed debugging on F5. After adding it (or removing request filtering) everything works fine.

附言描述了许多其他可能出现类似错误的问题 这里

P.S. A lot of other possible problems with similar error is described here