Hello
Can you check whether there is some details about the error in the worker's log?
Alternatively (and better), try running sysinfo on the source from command line and post the results. Sysinfo util can be found where converter server is installed, e.g. in "C:\Program Files (x86)\VMware\VMware vCenter Converter Standalone" as vmware-sysinfo-lin32.tar.gz or vmware-sysinfo-lin64.tar.gz. After untaring on the source, run vmware-sysinfo-lin64.sh.
Regards