I have taken backup database in ASA 8.0 using command line:
dbbackup -c "dsn=<dsn name>;uid=dba;pwd=sql" -y -d d:\backup.

-d option is used to take backup of database file only.

On trying to start backup database, it throws following error:
"cannot open transaction log file -- No such file or directory".

On providing a log file it throws following errors:
1. "Cannot open transaction log file......... Cannot use log file since it is shorter than expected."
2. "Cannot open transaction log file......... Cannot use log file since database file has been used more recently."

It is required to take backup of database file only due to large size of log file and we cannot truncate log file for doing synchronization.