I think I found what the issue is.
It is related to Solaris 10 OS patch level (http://sunsolve.sun.com/search/document.do?assetkey=1-21-141444-09-1), in the servers where the java 5 and 6 worked, the following files where patched.

Since my java application is using PKCS11 I'm guessing this is related. Now I need to patch the non-working servers to this level and see if it solve my issue.