What is the full stack error?
I came across the same problem this today (error suddenly popped up and not being able to find the solution which I know I found before via search), but thankfully had saved off the problem/resolution in a text file. Here's the magic that worked for me:
This means that the Hypersonic database (the internal datastore that handles JMS messages) has become corrupt. To fix this problem, shutdown all @task servers in the cluster and delete the contents of the JBOSS_HOME/server/default/data/hypersonic directory. These files will be recreated once JBoss is restarted.
Here's a little more of the stack for others to see:
10:44:05,087 WARN [ServiceController] Problem starting service jboss:database=localDB,service=Hypersonic
java.sql.SQLException: User not found: SA
at org.hsqldb.jdbc.Util.sqlException(Unknown Source)
at org.hsqldb.jdbc.jdbcConnection.(Unknown Source)
at org.hsqldb.jdbcDriver.getConnection(Unknown Source)
at org.hsqldb.jdbcDriver.connect(Unknown Source)
That solved it. Thanks much! Once again, user forums ROCK!