Activation codes are only for perpetual license. Did you just get Acad LT 2018?
If you did, activation is per the named account and not with any activation code. The use of the product must be assigned to your Autodesk Account/ID. As @natasha.l pointed out, reset or follow these steps:
Please note, folders of C:\Programdata and C:\Users\[Username]\Appdata (listed below) are hidden folders and you may need to adjust your viewing settings.
First make sure you're signed out of the desktop app and A360 (both are located in your Windows system tray
On your computer, navigate to
2017 Version: C:\ProgramData\Autodesk\CLM\LGS\<Product_Key>_2017.0.0.F [<Product Key> is the product key of the application you have]
2018 Version: C:\ProgramData\Autodesk\CLM\LGS\<Product_Key>_2018.0.0.F [<Product Key> is the product key of the application you have]
Delete the LGS.data file.
Navigate to C:\Users\[username]\AppData\Roaming\Autodesk\ folder
Delete the ADUT folder and it's contents
When you start the application, it will prompt you to choose one (that matches your license) of the following:
Login - 30 day trial or CLIC (Cloud Based) licenses
Serial Number - Students, Standalone and Single-User Term Based activation
Network - Network License server for obtaining licenses from a machine on your network
Good luck and report back on your progress
Mark Lancaster
& Autodesk Services MarketPlace Provider
Autodesk Inventor Certified Professional & not an Autodesk Employee
Likes is much appreciated if the information I have shared is helpful to you and/or others
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