I've downloaded all the possible manuals and documents related to troubleshooting, but I couldn't find anything about this conversion issue which could mean that it's either a local error or a bug in the application. The developers don't offer anything related to the conversion phase. I simply recommend repeating the operation you were doing at that time, maybe it will work.
Secondly, since the software doesn't appear available, follow the link to get in touch with the developers to ask for support: http://www.zkteco.com/support/Trouble_Ticket/37_48.html