We were sporadically seeing the exception:

Class ognl.OgnlRuntime can not access a member of class java.util.Collections$UnmodifiableList with modifiers "public"

In our production code trying to call "get" against an unmodifiable list. We've fixed it by commenting out OgnlRuntime:534.

It seems that 2 threads would enter invokeMethod. Both would call setAccessible(true). The first thread would call the method, then setAccessible(false). Then the second thread would try to call the method but, alas, no more accessibility.

Commenting out the line might be cheating, but, at least for our app, there seemed to be very little reason to set the accessibility back to false.