Then it is not clear what the problem is. I could suggest you try 5.1 but there is good chance the problem persists. Pls upload the logs for examination. As it seems there is no started task, you can get them from %ALLUSERSPROFILE%\VMware\VMware vCenter Converter Standalone\logs (or %ALLUSERSPROFILE%\Application Data\VMware\VMware vCenter Converter Standalone\logs for XP/2003)
Regards,
Plamen