ORA-12162: TNS:net service name is incorrectly specified

SQL> conn / as sysdba

ERROR:

ORA-12162: TNS:net service name is incorrectly specified

[oracle@micr~#] export ORACLE_SID=micrdb

[oracle@micr~#] sqlplus /nolog

SQL*Plus: Release 11.2.0.1.0 Production on Sun May 27 14:08:20 2013

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SQL> conn / as sysdba

Connected to an idle instance.
SQL>startup