If you are performing V2V conversion (the source VMs are powered off) then there *should* be some information in the worker log file. You can collect it manually from "%ALLUSERSPROFILE%\Application Data\VMware\VMware vCenter Converter Standalone\logs" directory. You can also try to switch the worker logging to verbose (instructions how to do it can be found at VMware KB: Increasing the logging levels to verbose for vCenter Converter application components) *and restart the worker service*.
If the source VM is powered on, then both the worker log (from Converter Server machine) and the agent log (from the source machine) should be provided.