Oracle Message PGA-20950 - unable to perform string on transaction log

ERRORunable to perform string on transaction log
CAUSEThe gateway server was unable to insert, update, or delete a pending transaction row in the transaction log table. An Oracle server message will follow this message.
ACTIONEnsure that the Oracle server and its TNS listener are both operational. Also check the PGA_LOG_DB, PGA_LOG_USER, and PGA_LOG_PASS parameters in the gateway init file and ensure that they specify the correct database string, userid, and password, respectively. Verify that the transaction logging PL/SQL stored procedure and the transaction log table have been properly installed into the Oracle server under the userid and password specified by PGA_LOG_USER and PGA_LOG_PASS. Refer to the Oracle Server Message and Codes Manual for information on the Oracle server message.