AFAIC the Migrate your PC... function in VMware Fusion is a half baked implementation of VMware vCenter Converter Standalone and is often problematic for some uses to get a connection between the source and destination and I'd never use it under any circumstances whatsoever. Instead I properly* prepare the source system for imaging and use VMware vCenter Converter Standalone saving the Virtual Machine to an external drive and transfer from there if I wanted the VM on the internal disk on the Host system.
* "properly* prepare" can take on different scenarios however generally speaking with a Windows source as an example at a minimum run Disk Cleanup before imaging. If the intent is to no longer use the physical machine and also have its user data actually reside on the Host's File System then prior to creating the Virtual Machine I'd make a separate backup and transfer of the User Data and then delete it from the source. Additionally I'd zero-out the free space after the remaining clean up. Then install VMware vCenter Converter Standalone on the source system and while walking through the Wizard make appropriate choices to create a right-sized and type virtual hard disk. If the VM is going to be stored/transferred/run from a external hard drive that is formatted FAT32 then make sure you split the virtual disk in 2 GB segments. Also if there will be limited free space on either internal or external storage using a split disk will facilitate snapshot removal and shrinking/cleaning up the virtual dial as the VM is used even if its filesystem can handle the size of a monolithic type disk from a initial storage capacity. Additionally after cleanup and before installing VMware vCenter Converter Standalone I'd Defrag the source if it's using an HDD vs. an SSD.
Obviously there are other scenarios however the main thing it to think through the process before beginning so as to optimize the end results with expending the least energy and effort and starting with a clean source is usually easier and faster then having to cleanup a VM created of an unprepared source system.