Please make sure to type in the Virtualization Packager license key (including dashes) or copy & paste. If it doesn't work still, i would suggest to raise a support ticket with VMware.
Which do you use the version of Windows 10 ?
As far as I know, this license error occurs on Windows 10 ver.1803.
ThinApp 5.2.3 does not support Windows 10 ver.1803. You should evaluate ThinApp 5.2.3 on previous Windows version 1709.