I've got the same issue with JBoss 6.4 EAP. Did you find any solution?
It's trying to cast a org/springframework/web/servlet/support/JstlUtils$SpringLocalizationContext into a java/lang/String . This is due to that the JSTL implementation doesn't recognize SpringLocalizationContext as a LocalizationContext instance though SpringLocalizationContext surely implements the interface. The root cause is that two classes are loaded from different classloader thus the instanceof check failed.
This appears to be a conflict due to the presence of same versions of jstl jars in the different distribution.
Note: Do not include same jstl 2 jar files in your application (war file).
Thanks Anup. My problem has disapeared after some maven clean install and redeployment from my IDE.