A few suggestions:
1. Double-check to make sure the location X-Plane is installed to isn't system-owned. This can interfere with X-Plane's ability to read and write files correctly.
2. Disable any and all anti-virus software that may be running. These can interfere with X-Plane in the same way, by preventing the plugin from running correctly.
3. Another possibility involves your computer's network MAC address. The activation key file is generated using a number of inputs, which includes the MAC address. If you use multiple network cards, the order in which they are loaded may change from one reboot to the next, which can cause the copy protection in SASL to detect that the MAC address has changed and that it needs to be activated again.
We recommend disabling all but one network card, to ensure you have the same MAC address from one boot to the next.
4. Additionally, using VPNs or similar software may cause a similar error. We also recommend disabling any VPN while troubleshooting this, to eliminate that possibility.
5. If you run the "X-Jet" plugin, be sure to update to the latest version. An old version of this plugin used to cause this reactivation issue.
6. Plugging or unplugging USB devices (headsets, memory sticks, etc.) may change the hardware ID that SASL calculates, resulting in SASL asking for reactivation. This has been reported to the SASL plugin team, but for now try to keep the same USB devices plugged in between runs of X-Plane, and see if that helps.
7. Keep your SASL plugin updated.
If is still not working, please open a support ticket. If you need an activation increase, please include the serial number as well.