connection failed issue while login the application

I am using jboss 4.0.5 and ms sql 2005 in my application, actually i can login with 'sa' user but after 20 or 30 mins if i login with same 'sa' user am getting this connection fail issue.Below is my log details...Please help

2016-03-17 07:56:52,775 DEBUG [org.jboss.resource.connectionmanager.IdleRemover] run: IdleRemover notifying pools, interval: 450000 2016-03-17 08:04:22,784 DEBUG [org.jboss.resource.connectionmanager.IdleRemover] run: IdleRemover notifying pools, interval: 450000 2016-03-17 08:11:52,793 DEBUG [org.jboss.resource.connectionmanager.IdleRemover] run: IdleRemover notifying pools, interval: 450000 2016-03-17 08:19:16,708 WARN [org.jboss.resource.connectionmanager.JBossManagedConnectionPool] Throwable while attempting to get a new connection: null org.jboss.resource.JBossResourceException: Could not create connection; - nested throwable: (com.microsoft.sqlserver.jdbc.SQLServerException: Login failed for user 'sa'.) at org.jboss.resource.adapter.jdbc.local.LocalManagedConnectionFactory.createManagedConnection(LocalManagedConnectionFactory.java:179) at org.jboss.resource.connectionmanager.InternalManagedConnectionPool.createConnectionEventListener(InternalManagedConnectionPool.java:565) at org.jboss.resource.connectionmanager.InternalManagedConnectionPool.getConnection(InternalManagedConnectionPool.java:250) at org.jboss.resource.connectionmanager.JBossManagedConnectionPool$BasePool.getConnection(JBossManagedConnectionPool.java:491) at org.jboss.resource.connectionmanager.BaseConnectionManager2.getManagedConnection(BaseConnectionManager2.java:341)