Re-validate old e-signature error in Acrobat 9 but not in Acrobat XI.

We have 2 versions of Acrobat, 9 and XI. We are using e-certificate from Hong Kong Post (HK government). Each certificate has a validity of 3 years, after 3 years a new certificate will be assigned to the owner.

We have a user who used her e-certificate to sign a document in 2013, her certificate, back then, is vaild til 2015. When the old ceritficate past the last vaild date, she got a new one from Hong Kong Post.

When we try to open documents she signed in 2013 with Acrobat 9, it said the signature has expired and the little yellow triangle shows up when we validate the signature. When the same documents are opened by Acrobat XI, it said the signed signature is valid and when click into the detail, it said Signature is not LTV enabled and will expired after 2015.

I would like to know why it show the signature is not valid in Acrobat 9?

Thanks,

Richard