I went through the entire Support Forum and could find not help.
I have a Windows 10 desktop HP Envy i7 and a Windows 10 laptop Dell Inspirion 15 i5 that will not eject the PortableApps USB drive.
Inspection reveals that "eject.exe" file in %temp% folder is not being deleted (even when the USB_Eject_Cleanup.bat is executed in Admin)
Therefore, when I try to eject the USB PortableApps again I get the error popup:
Could not write to windows temp dir!
The program will now exit.