If you are on a network that is connecting to the internet through a proxy server you must follow these instructions in order to ensure that NinjaTrader license checking does not fail.
Open the file C:\Program Files\<NinjaTrader Folder>\bin\NinjaTrader.exe.config using MS Notepad or any other text editor
Replace the text "False" with "True"
Save the file
Restart NinjaTrader
NinjaTrader will now use your PC settings for the proxy server.