>If your recovery model is "Full" you must have full backup of the database and backup of the LOG to shrink the file.
>BTW there is no need to shrink the LOG.
>Autogrowth is a resource eating task. If you Backup the LOG SQL Server can reuse its space.

The recovery mode has been set to simple.

If I wouldn't have shrunk that log, we would have run out of disk space. This wasn't making any sense to have half a terabytes of log for our development and test environments. This grows indefinitely if there is no procedure to take care of that. I always have this shrunk at midnight to 1 MB to start all over.