Migration Assistant keeps failing at last hurdle.

Trying to migrate old Mac to Mac Mini. Using a Ethernet cable, every thing goes fine. After about four hours and data transfer complete I get a message saying “there is not enough free space to complete the migration”. There is it least 100GB available. Got close and took a few backward steps to take off some data to be transferred, then got a message about Flash on the old Mac. “Incompatible Software. This version of Flash Player is not compatible with this version on MacOS. Then I got the uninstaller from Adobe website, took out flash and restarted. Whole process all over again and four hours later still getting the “not enough free space” massage. So frustrating…