Oracle EXP error EXP-00056

When I was trying to run the EXP commnand as follows
EXP userid=username/pwd@sid file=d:\dumps\20080113_1.dmp log=d:\dumps\20080113_1.log tables=(pm1,pm2,pm3,pm4,pm5a,pm5b,pm6)

got this error:

EXP-00056: ORACLE error 12560 encountered
ORA-12560: TNS:protocol adapter error
EXP-00000: Export terminated unsuccessfully

Found the following to solve my misery; just remove the @sid ! And it worked.

EXP userid=username/pwd file=d:\dumps\20080113_1.dmp log=d:\dumps\20080113_1.log tables=(pm1,pm2,pm3,pm4,pm5a,pm5b,pm6)

Have a bug free day :)