1 connection to linux (centos58-64) slave does not start, looping forever. Logs are empty.
1 connection to windows (win7-32/cygwin) slave does not start, looping forever. Logs are empty.
1 connection to windows (win7-64/cygwin) slave does not start, looping forever. Logs are empty.
1 connection to linux (centos58-32) slave is working after removing and creating a new slave config...
1 connection to max (Mac OS X) slave is working after removing and creating a new slave config...

Issue impossible to fix because of the lack of information (empty log).

All the connections worked well before upgrading to Jenkins V 1.591 and SSH Slaves plugin V 1.9. Now, reverting to older versions does not fix the problem.