Oracle: ORA-12519, TNS:no appropriate service handler found on application processing

When running application on SUN application server, it suddenly gets "ORA-12519, TNS:no appropriate service handler found" error message when view a page. Sometime page will show up but sometime it gets error.

SOLUTION: under command window. RUN:
lsnrctl services
at 9/02/2008 10:59:00 PM