Truncating logs doesn`t work

Hi everyone...

Using SQL Server 6.5 Enterprise Manager, I truncated the log with no success. The availability of the log is the same even after I click on the Recalculate button...Sometime if I click on the Truncate button, it goes down to zero.The database has "trun. log on checkpoint" option. Both the database and the log are in different devices. In the device view for the log, it shows a negative number and I cannot change it..I have applied Service pack 4 for SQL server already..and it still doesn`t work. Have anyone seen this?

Any suggestion is appreciated....
binh
bth@prucka.com