Hello
Let me check if I understand correctly - 2 partitions on the destination machine are empty, the corresponding source volumes are fine, correct?
Is it possible the source volumes are encrypted? If so, they can't be converted. As a workaround, you could copy their files manually (network share, FTP,..)
If that's not the case, the interesting log is the agent's one. It is located on the source machine, in "%ALLUSERSPROFILE%\Application Data\VMware\VMware vCenter Converter Standalone\logs"
HTH
Plamen