This might help.
Remove all the listner services from the service manager.
In the registry HKEY_LOCAL_MACHINE/SOFTWARE/ORACLE create a string named TNS_ADMIN with value as the full path name where listner.ora file exists
Create a new listner by running lsnrctl. ( ur path should be proper if u have 2 or more oracle homes).
After the listner service has started, see if the proper listener.ora file is getting pointed to or not. ( can check this using the status option at the lsnrctl prompt. )..
Try connecting to the database after this...this may help as this was the error I was getting when doing a migration and the above procedure did solve the problem.
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