There are two known compatibility issues between Enterprise Server v2.1.1 and Java ES 5 (JES5).
The JES5 Service Registry is not compatible with Enterprise Server v2.1.1 because of the JSF 1.2 version provided by Enterprise Server v2.1.1. The Service Registry needs to be upgraded to JES5u1 prior the Enterprise Server upgrade to v2.1.1. This limitation is also documented in the Service Registry documentation.
The JES5 Portal Server is not compatible with Enterprise Server v2.1.1 because of the JSF 1.2 version provided by Enterprise Server v2.1.1. Portal Server needs to be upgraded to JES5u1 prior the v2.1.1 upgrade to v2.1.1.
On a Java ES 5 setup that has Portal Server on Enterprise Server 8.2, upgrading Enterprise Server 8.2 to v2.1.1 makes the Portal Server unusable. Enterprise Server v2.1.1 uses JSF 1.2, but the JSF-Portlet bridge in Release 5 Portal Server does not support JSF 1.2. On Solaris/Linux the Portal Server needs to be upgraded to JavaES5 Update 1. On Windows do not upgrade Enterprise Server to v2.1.1 if you want to continue using the Release 5 Portal Server, as Portal Server is not supported in Java ES 5 Update 1 on Windows.