PROBLEM:
Your SQL transaction log has grown to be really big, this might be because a load of data was added, or your backup procedures were failing to truncate the logs.
SOLUTION:
Take a backup of the database, then open the SSMS and then run this command:
USE DATABASENAME
GO
ALTER DATABASE DATABASENAME SET RECOVERY SIMPLE WITH NO_WAIT
DBCC SHRINKFILE(DATABASENAME_log, 1024)
ALTER DATABASE DATABASENAME SET RECOVERY FULL WITH NO_WAIT
GO
Now take a full backup of the database to ensure you have a recoverable version.