Help! ORA 01012 WHEN execute SELECT DBMS_FLASHBACK.GET_SYSTEM_CHANGE_NUMBER

Question

I encounter ORA 01012 WHEN execute "SELECT DBMS_FLASHBACK.GET_SYSTEM_CHANGE_NUMBER FROM DUAL;" in my ProC program, but under SQLPLUS it is ok. The whole scenarios are:
1. My platform is Solaris 10, Oracle 10.2g / 64bit
2. "alter system archive log current" failure, Oracle complaint about flash_recovery_area full, so I run
delete obsolete;
crosscheck backup;
delete expired backup;
3. Later I issued command "shutdown", oralce had no reponse after long time, so I issued command "shutdown abort" to shutdown the database, and then "startup" the database successfully to "READ WRITE", user application can also accessed the database.
4. One of my ProC program get ORA-01012 when execute SELECT DBMS_FLASHBACK.GET_SYSTEM_CHANGE_NUMBER FROM DUAL;
5. But I got no error if I execute "SELECT DBMS_FLASHBACK.GET_SYSTEM_CHANGE_NUMBER FROM DUAL; " using SQLPLUS.
Any suggestion about this problem? blow is my ProC function call.
u_int32_t
proc_GetLastSCN()
char buf[300];
u_int32_t scn=0;
if (proc_ConnectDB() == APP_ERROR)
return APP_ERROR;
memset(buf, 0, sizeof(buf));
snprintf(buf, sizeof(buf),
"select DBMS_FLASHBACK.GET_SYSTEM_CHANGE_NUMBER from DUAL");
oraca.orastxtf = ORASTFERR;
EXEC SQL WHENEVER SQLERROR GOTO ora_sqlerror;
EXEC SQL WHENEVER NOT FOUND DO break;
EXEC SQL WHENEVER SQLWARNING CONTINUE;
EXEC SQL PREPARE S5 FROM :buf;
EXEC SQL DECLARE C5 CURSOR FOR S5;
EXEC SQL OPEN C5;
for (;;) {
EXEC SQL FETCH C5 INTO :scn;
EXEC SQL CLOSE C5;
proc_DisconnectDB();
return scn;
ora_sqlerror:
dyn_error("ORACLE error --proc_GetLastSCN\n");
EXEC SQL CLOSE C5;
proc_DisconnectDB();
return 0;
int32_t
proc_ConnectDB()
/* Declare variables. No declare section is needed if MODE=ORACLE. */
VARCHAR username[DB_MAX_NAME_LEN];
/* VARCHAR is an Oracle-supplied struct */
VARCHAR password[DB_MAX_NAME_LEN];
int32_t ret = APP_OK;
strncpy((char *) username.arr, gateinfo.szSrvLogin, sizeof(gateinfo.szSrvLogin));
username.len = (unsigned short) strlen((char *) username.arr);
strncpy((char *) password.arr, gateinfo.szSrvPassword, strlen(gateinfo.szSrvPassword));
password.len = (unsigned short) strlen((char *) password.arr);
EX_SCREEN_INIT();
EXEC SQL WHENEVER SQLERROR GOTO ora_sqlerror;
EXEC SQL CONNECT :gateinfo.szSrvLogin IDENTIFIED BY :gateinfo.szSrvPassword;
return ret;
ora_sqlerror:
errlog(ELOG_ERROR, "proc_ConnectDB@Failed to connect to %s!", gateinfo.szHistSrv);
sql_error("ORACLE error proc_ConnectDB --\n");
ret = APP_ERROR;
return ret;
}

Answer 1

01012, 00000, "not logged on"
// *Cause:
// *Action:use COPY & PASTE so we can see what you do & how Oracle responds.