Are you sure that adding a column directly to the database is the
right way to do it in your application? Some applications use
configuration files to store DB schema info, you change the
configuration file and DB schema gets auto-regenerated. If your
application follows this pattern, you just need to find and modify the
appropriate configuration file to fix the problem.
Another easy solution I can think of is restarting your application/
SQL server/computer. As silly as it sounds, it might work: sometimes
the error is caused by cached old schema, restart invalidates the
cache and the problem disappears.