another useful hint:
if you are getting this exception when you are using a JDBC Realm
[#|2007-11-04T23:08:10.046+0100|SEVERE|sun-appserver9.1|javax.enterprise.system.core.security|_ThreadID=13;_ThreadName=httpSSLWorkerThread-8080-1;webuser;_RequestID=7f18238c-d368-4144-b63e-fcf11ea11dba;|SEC1111: Cannot load group for JDBC realm user [webuser].|#]
make sure the column for the user name in your user table is named identically as the column for the user name in your group table.
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