Unable to login

When users are trying to login into oracle applications they are unable to login.
It shows the following error
oracle.apps.fnd.framework.OAException: Application: FND, Message Name: SQL_PLSQL_ERROR. Tokens: ROUTINE = createSession(int)(userId=6,sessionMode='null','4DE538960900125FE040A8C00A016CCC24684017652941783825214968716732'); REASON = java.sql.SQLException: ORA-20001: Oracle error -20160: ORA-20160: Encountered an error while getting the ORACLE user account for your concurrent request.
Contact your system administrator.ORA-06512: at "APPS.ALR_FND_USER_UAR", line 1ORA-04088: error during execution of trigger 'APPS.ALR_FND_USER_UAR' has been detected in FND_SIGNON.NEW_ICX_SESSION.ORA-06512: at "APPS.APP_EXCEPTION", line 70ORA-06512: at "APPS.FND_SIGNON", line 18ORA-06512: at "APPS.FND_SIGNON", line 490ORA-06512: at "APPS.FND_SESSION_MANAGEMENT", line 318ORA-06512: at "APPS.FND_SESSION_MANAGEMENT", line 455ORA-06512: at line 1; ERRNO = 20001; (Could not lookup message because there is no database connection) at oracle.apps.fnd.framework.server.OAExceptionUtils.processAOLJErrorStack(OAExceptionUtils.java:974) at oracle.apps.fnd.framework.OACommonUtils.processAOLJErrorStack(OACommonUtils.java:866) at oracle.apps.fnd.framework.webui.OAPageBean.validateUser(OAPageBean.java:4572) at oracle.apps.fnd.framework.webui.OAPageBean.preparePage(OAPageBean.java:687) at oracle.apps.fnd.framework.webui.OAPageBean.preparePage(OAPageBean.java:497) at oracle.apps.fnd.framework.webui.OAPageBean.preparePage(OAPageBean.java:418) at _oa__html._OA._jspService(_OA.java:88) at oracle.jsp.runtime.HttpJsp.service(HttpJsp.java:119) at oracle.jsp.app.JspApplication.dispatchRequest(JspApplication.java:417) at oracle.jsp.JspServlet.doDispatch(JspServlet.java:267) at oracle.jsp.JspServlet.internalService(JspServlet.java:186) at oracle.jsp.JspServlet.service(JspServlet.java:156) at javax.servlet.http.HttpServlet.service(HttpServlet.java:588) at org.apache.jserv.JServConnection.processRequest(JServConnection.java:456) at org.apache.jserv.JServConnection.run(JServConnection.java:294) at java.lang.Thread.run(Thread.java:534) ........
...........

O.S. - HP-UX

Solution:
To implement the solution, please execute the following steps:

Disable the trigger 'ALR_FND_USER_UAR' using sqlplus :

- SQL> alter trigger ALR_FND_USER_UAR disable;

- Retest Login.


Metalink suggest the following doc id's solution:
1) Note:388695.1
2) Note:357998.1
And Bouncing the Apache could resolve the error in some cases.