From your appserver, can you telnet to the virtual machine on port 4750?
i.e. telnet server_name 4750
If that doesn't work, then there's either a route missing, or a firewall rule somewhere preventing traffic... You should verify that with your network admins if it's the case.
Also make sure that the target name as entered in BladeLogic is a hostname that the appserver can resolve. You can't enter something like "Virtual_Machine_1" if that is not an actual hostname your appserver can resolve...
Target names must be either valid hostnames, or ip addresses