It does look like you have used both your Desktop activations already (as well as both your Web license activations too).
When you open the License Key Window in Xojo do you see your license listed there?
Yes -> Then make sure your build settings aren't set to build for a platform your license doesn't support. (like trying to build for iOS with a Desktop license.) Also, make sure you aren't trying to access a feature your license doesn't include, like linking to a database other than SQLite with a Xojo Lite license.
No -> Sign In to Xojo with the Xojo username and password you used when you purchased. If you can't download your license to the Xojo IDE, go to your license key page at the Xojo website and verify you haven't used all your activations already. Click the 'x" next to a machine to deactivate your license from that machine. This frees up an activation for a new machine. Then, Sign In to the Xojo IDE on the new machine to activate your license there. Make sure to use the same Xojo ID that you used when you purchased. Remember, Xojo Lite licenses allow for 1 activation at a time, Xojo Desktop, Web & iOS licenses allow for 2 and Xojo Pro and Enterprise allow for 3.
If you have any further trouble or get that error again, please email me at firstname.lastname@example.org and let me know what release you are using and on what platform and I'll look into it further.