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Make sure that your computer is connected to the internet.
Verify you are logged into an Administrator account on the computer.
Sometimes, security software such as anti-virus, anti-malware, or firewall software, can block a program's access to the internet.
Make sure that security and firewall software are set to allow communication from your TI-Nspire or TI-SmartView software to the Internet.
WHAT ARE SOME THINGS YOU CAN TRY WHEN A CUSTOMER REPORTS ERROR CODES S21, S22, S23, S24, S25, S26, S27, S99, P21, P22, P23, P24, P25, P26, P27, P28, P99, A0, or A14
Which usually indicate problems connecting with Texas Instruments' activation server.