Review database connection issues.
               The following are the common Oracle Database connection error codes, their causes, and suggested remedies.
               
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                        TNS-12203
                  
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                     TNS: unable to connect to destination 
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                     Cause: OracleServiceSID service, OracleHOMENAMETNSListener service, or both are not running.
                      
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                     Action: Ensure that both services are started.
                      
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                        ORA-12560
                  
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                     TNS: lost contact 
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                     Cause: OracleServiceSID service, OracleHOMENAMETNSListener service, or both are not running. You receive this error if you attempt to use any Oracle Database utilities, such as SQL*Plus. This error is analogous to the following Oracle7 error: ORA-09352:Windows32-bitTwo-Taskdriverunableto spawnnewORACLEtask.
 
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                     Action: Ensure that both services are started.
                      
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                        ORA-28575
                  
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                     unable to open RPC connection to external procedure agent  
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                     Cause:
                        tnsnames.ora andlistener.orafiles have
                        not been correctly configured to use external procedures.
 
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                     Action: Reconfigure services.
                      
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                        ORA-06512
                  
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                     at "APPLICATIONS.OSEXEC", line 0 
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                     Cause: tnsnames.ora and listener.ora files have not been correctly configured to use external procedures.
 
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                     Action: Reconfigure services.
                      
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                        ORA-06512
                  
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                     at "APPLICATIONS.TEST", line 4  
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                     Cause: tnsnames.ora andlistener.ora files have not been correctly configured to use external procedures.
 
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                     Action: Reconfigure services.
                      
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                        ORA-06512
                  
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                     at line 2  
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                     Cause: tnsnames.ora andlistener.ora files have not been correctly configured to use external procedures.
 
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                     Action: Reconfigure services.
                      
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                        ORA-01031 and LCC-00161
                  
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                     Both codes appear at startup 
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                     Cause: Parameter file (init.ora) or Windows services are damaged. These errors usually appear when the parameter file cannot be read by Oracle Database at database startup. 
                      
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                     Action: Delete and re-create the SID and services. Make sure you are logged on as the user Administrator, or a user within the Windows Administrator's Group with full administrative rights. At the command prompt, enter: oradim -delete -sid sidwheresidis the name of your database (for example,orcl). Re-create the SID and services by entering:oradim -new -sid sid -startmode auto -pfile full_path_to_init.ora