You might try (temporarily) disabling security products like antivirus, antispyware and anything offering "Internet Protection" or security.
Disable the Vista firewall at the service level. (Start, Run, services.msc, find Windows Firewall, double-click, stop and change startup type to Disabled)-OK this one probably isn't really for you, but I put it in for the person who finds this thread with a search and has a more basic connectivity problem.
Sometimes uninstalling all versions of java, restarting and then installing the latest version from java.com helps.
Have you run a checkdisk yet? It could be caused by disk corruption.
If none of those work you might actually have a bit of malware interfering with mafia, use SuperAntiSpyware or MalWareBytes to do a full scan and clean.
It could also be Vista's Data Execution Prevention, to turn that off from a command line type "bcdedit.exe /set {current} nx AlwaysOff"