i am having similar problems deploying an .ear with a utility.jar file
it seems that some of the classes are visible to the application and some are not.
it is strange. there are many posts on this issue and nobody ever replies back.
if you've figured out anything, let me know.
Do you have the application.xml config'd correctly in the ear's WEB-INF?
Where are you putting your cactus.jar?
Did you put it under WEB-INF/lib?
FYI, libraries and classes that are used by servlets or JSPs, ought to be put under WEB-INF/lib and WEB-INF/classes directories.