vCenter Converter 6.0 is the last release that support Acronis images, see: https://www.vmware.com/support/converter/doc/conv_sa_60_rel_notes.html#interop
VMware vCenter Converter Standalone 6.0 Support Notice
VMware vCenter Converter Standalone 6.0 is the last release of the product to support third-party backup images and virtual machines as sources for conversion. This capability will be discontinued in the next release. If you use this capability, you should start planning your transition.---
Senior Infrastructure Specialist
Thank you, Richardson
I hadn't seen that (VMware.com is something of a maze).
I still have a copy of my original installation - VMware-converter-en-5.5.3-2183569.exe - so I'll revert to that.
Odd - many SME/SB & corporate customers use Acronis, so VMware may be cutting its own throat to some extent.