Without knowing the version of ESXi it could be an issue with the SSL protocol being used.
Give this a go to see if it works. Change the value of 123422720 in the <sslOptions> tag to 56313856 in the following files.
- converter-server.xml
- converter-worker.xml
- converter-agent.xml
- converter-client.xml
Path to files (may vary depending on OS)
- C: \ ProgramData \ VMware \ VMware vCenter Converter Standalone
- C: \ Program Files (x86) \ VMware \ VMware vCenter Converter Standalone
Kind regards.