sap transaction log backup error

Hi Experts,

In Sybase database, I am able to take database backup but while taking the transactional backup it is showing error.

i followed process for Database backup is

step 1: isql -Usapsa -X -S<SID>

step 2: Password

step 3:dump database <SID> to "File name.dmp"

step 4:go  ,enter

and for transactional backup,

step 1: isql -Usapsa -X -S<SID>

step 2: Password

step 3:dump tran <SID> to "File name.dmp"

step 4:go  ,enter

i think it is correct but it is getting error ,please tell me what is the reason ,and how to solve.The error message is shown below image.

Thanks & Regards,

Patan Thavaheer.