Upon more careful examination, it occurs that the NFC connection has timed out. I was wrong about the registry.
This is most probably related to the destination ESX host rather than to converter. You may ask in a vSphere forum eventually.
I am not aware of any limitation related to 10TB (ESX 5.5 supports up to 63 IIRC).
That said, here are some guesses that could hopefully work around the issue.
You may try increasing the timeout intervals. For converter side - edit converter-worker.xml an look for <readTimeoutMs>. The default is 2min, try something bigger, e.g. 10min. Restart converter worker service after the change. This xml file can be found in "%ALLUSERSPROFILE%\VMware\VMware vCenter Converter Standalone".
This KB is about NFC timeouts on the ESX: http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=2038497
Take into account there are 2 NFC servers in an ESX host - hostd and vpxa. When the conversion targets an ESX host directly, it uses hostd (what you have done), when it targets a vCenter Server, it uses vpxa. The KB is about vpxa; for hostd you shoud edit its configuration file (it shouldn't be difficult to find it)
You may also eventually try converting through vCenter Server. There used to be some differences between the two servers at some point of time which should have been fixed, but I am not an expert in NFC.
As for the many disks limitation - here is an interesting idea for workaround:http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1012211
HTH
Plamen