If the $35 price tag is genuinely out of reach for a hobbyist or student, do not use cracked software. Use one of these alternatives:
If the software is locked and won't let you overwrite the bad key, you can manually clear the stored license data to revert the software back to evaluation/trial mode or input a fresh, valid key: On Windows: Close Beyond Compare. %APPDATA%\Scooter Software\Beyond Compare 4\ beyond compare 4 license key has been revoked