It is found that within the installation of JBOSS EAP 5.1.1, some libraries have different version.
For example:

.././jboss-eap-5.1/seam/lib/jboss-deployers-client-spi.jar has the version 2.0.0 Beta6

However

.././jboss-eap-5.1/jboss-as/lib/jboss-deployers-client-spi.jar has the version 2.0.10GA

In the same release, ideally the same library within the same EAP installation should have the same version.
Here are the list that I found so far for reference:

jboss-deployers-core-spi.jar
jboss-deployers-client-spi.jar
bsh.jar
commons-logging.jar

• As it is visible that the "../seam/lib" directory is containing the JARs which contain different versions, hence I would request to make sure that the JARs shipped within "../seam/lib" directory should have the same version which are also present in "$JBOSS_HOME/common/lib" or "$JBOSS_HOME/lib" etc.