Remote exception in JBoss

[shoa]

Hello

I have a Java server using JBoss and a database (mySQL). I also create an
application with some SessionBeans. My application run OK. However,
sometime, the application does not run as there is a remote exception. There
error is:

Remote Exception : RemoteException occurred in server thread; nested
exception is:
java.rmi.ServerException: EJBException:; nested exception is:
javax.ejb.EJBException: null; CausedByException is:
No ManagedConnections available within configured blocking timeout ( 30000
[ms] ); - nested throwable: (javax.resource.ResourceException: No
ManagedConnections available within configured blocking timeout ( 30000
[ms] ))
Remote Exception while generating myBeans //

Then I have to restart the server (JBoss) to make my application to run
again....

I know that there are many reasons for this errors. If you have any clue,
please help!!!

Thank you
S.Hoa