I have an HTC One M9, I can tether a laptop via USB cable, and an iPad via Bluetooth, but the Portable Wifi Hotspot will not allow connection from either. I have renamed the SSID and set a new access key, but still no joy. Any suggestions?
You should check the advanced settings for compatibility with the Security protocol between the devices. By default it should be Wpa2(aes). Change it and try parring again.
Advanced settings is in the top right corner in hotspot settings menu.