ORA-12154: TNS:could not resolve the connect identifier specified

Hello Friends,
I am using Oracle10.1.0.2.0. While tacking a backup I get following error.

EXP-00056: ORACLE error 12154 encountered
ORA-12154: TNS:could not resolve the connect identifier specified
EXP-00000: Export terminated unsuccessfully

Please refer to the attached image for detail.

isnt it obvious? the database name cannot be resovled via tns - sort out your tns issues

Also, since you cannot recover a crashed database from an export, an export is not a backup