This error i have seen a few times.
You need to Trunk your log file:
Following databases have large amounts of space allocated on the disk but not in use. This may be due to recent deletion of data form the database, or because the database has been pre-grown to a larger size. This database will take up a larger amount of space on the file system unless it is shrunk down to a smaller size.
Do this following:
Backup your DB,
Change recovery mode to simple
Right click on the DB it is warning you about and select Shrink and database
You can also do a Transaction log backup which should truncate it.
If you just need to shrink your Log file choose files and select Log File