If you use 5.5.3, run it only on Windows 7 or Server 2012 R2 with VMware Workstation 10.x or ESXi 5.5 . For anything newer, switch to Converter 6.x or a modern P2V tool.
💡 (still free) from VMware’s website (Broadcom portal account required). vmware-vcenter-converter-standalone-5.5-3