If you are trying to upgrade Windows 7/8 to Windows 10 and you get this error, don’t Panic 🙂
Simply use a Disk Manager (many are free like the excellent MiniTool Partition Wizard)
Available here: https://www.partitionwizard.com/download.html
Extend the 100Mb DATA Partition to approx’ 500MB (Making it 500Mb sets it up ready for future updates including the latest Creators Update)
After rebooting you should be good to go 🙂
BTW, you can stil get the FREE upgrade if you use any of the MS Assistive Technologies 🙂
Simply go here, download the file and run it, you may need the info above if you have a small SSD/HDD
https://www.microsoft.com/en-us/accessibility/windows10upgrade