Navigate to the (usually C:\Program Files (x86)\Labcenter Electronics\Proteus 8 Professional ). Look for a subfolder named Bin . Find an executable named LICENCE.EXE (or similar). Right-click it and select Run as Administrator .

Add the Labcenter Electronics folder to your .

The "Cannot find a valid license key" error is almost always a communication breakdown between the and the License Manager . By ensuring you are running the program as an administrator and verifying that the keys are actually installed in the License Manager tool, you can resolve 90% of these cases.