I did the following

1. Change the recovery model to simple

2. issue the commnad backup log <DB Name Here> with truncate_only. But this time file size not changed. FIle size is still 10 gb . But uses only 25 MB

3. When i try to reduce the log size using enterprise manager, sql showing message "error 21335, New DB File size must be larger than current size'

Pls explain me how can i reduce the physicial Transaction  file size

Mathew