1. Self-employed certificate expired: self-employed certificate expired, and signature verification cannot be performed. You need to update the self-employed certificate and ensure that the certificate has not expired.
2. Self-employed certificate is damaged: the self-employed certificate is damaged, and signature verification cannot be performed. You need to regenerate the self-employed certificate and make sure that the certificate is not damaged.
3. System problems: Sometimes, system problems may also lead to signature verification failure. You can try to restart the system or update the system software to solve the problem.
4. Browser problems: If you encounter problems when using the browser for signature verification, it may be because the browser version is too old or the browser settings are incorrect. You can try updating your browser or checking your browser settings to solve the problem.
If the above methods can't solve the problem, I suggest you contact relevant departments or professionals for further help and guidance.