Problem with the connection

Hi,

I do encounter this error

OLE DB provider "OraOLEDB.Oracle" for linked server "ORA_CONN" returned message "ORA-12518: TNS:listener could not hand off client connection".

Msg 7303, Level 16, State 1, Line 2

Cannot initialize the data source object of OLE DB provider "OraOLEDB.Oracle" for linked server "ORA_CONN".

on the connection, on which I have a linked server, within Sql server, pointing to Oracle DB. How to resolve this?