As Satnam already mentioned, restarting the SQL Server will clear up the log space used by tempdb.

If this however is not an option, you can try the following:

* Issue a CHECKPOINT command to free up log space in the log file.

* Check the available log space with DBCC SQLPERF('logspace'). If only a small percentage of your log file is actually been used, you can try a DBCC SHRINKFILE command. This can however possibly introduce corruption in tempdb.