PKIX path validation failed: java.security.cert.CertPathValidatorException : timestamp check failed

Hi,

I am getting the following exception when a webservice callout is made.

System.CalloutException: IO Exception: sun.security.validator.ValidatorException: PKIX path validation failed: java.security.cert.CertPathValidatorException: timestamp check failed

Until few weeks ago the webservice callout worked fine.

And there has been no code change from that point.

Can anyone let me know what could be the exact cause why this error is encountered?

Thanks in advance.