This is same problem described in JBSEAM-2357. Under load the UnifiedELValueBinding sometimes throws an exception like the following. Need to backport the fix into Seam 1.2 enterprise branch.

Caused by: javax.el.PropertyNotFoundException: ELResolver cannot handle a null base Object with identifier 'identity'
at com.sun.el.lang.ELSupport.throwUnhandled(ELSupport.java:52)
at com.sun.el.parser.AstIdentifier.getValue(AstIdentifier.java:75)
at com.sun.el.parser.AstValue.getValue(AstValue.java:114)
at com.sun.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:195)
at org.jboss.seam.util.UnifiedELValueBinding.getValue(UnifiedELValueBinding.java:35)
at org.jboss.seam.security.Identity.evaluateExpression(Identity.java:518)
at org.jboss.seam.security.Identity.checkRestriction(Identity.java:160)