1. Check the signature file: make sure that the signature file has not been tampered with or damaged. You can try to use other tools or methods to verify the integrity of the signed file.

2. Check the signature process: carefully check every step in the signature process to ensure that there are no omissions or errors. For example, try to re-execute the signing process and ensure that each step is performed in the correct order.

3. Check the certificate or key: If you use a certificate or key for signature verification, please make sure it is valid and has not expired. Check the expiration date of the certificate or key and make sure that you have the correct certificate or key.

4. Check the system and network: check whether the system and network work normally. Make sure the system time and date are set correctly and the network connection is stable. Out-of-sync time or network problems will cause signature verification to fail.