"will this install keep the existing license code?"
You would need to create a user (you don't have to fund an account) and start a demo.
Then you can import a valid license key and continue using the features you are accustom to.
"when I try to import the license code on the web page I get an error: The license key you entered could not be imported. Please contact support"
Please send an email to platformsupport [at] ninjatrader.com and provide this error message and the license key you are trying to import.
A member of our Client Services team will be happy to assist.
"is 8.0.28.0 64-bit not being updated?"
8.0.28.0 is an out of date release and will have no further development, no security updates, or bug fixes.

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