MDN Not Signed Error

After updating a certificate in PI we are facing MDN not signed errors.

In Seeburger logs, I can see that the response MDN is signed.

However, Seeburger, doesn't find the signature and generates a negative MDN.

Unchecking the signature in the receiver AS2 channel fixes the problem.

This issue seems very similar to the following thread: Seeburger AS2 Adapter: "MDN not signed"

SAP PI Version : PI 7.11 SP12

Seeburger AS2 2.1.5

Original Certificate: 1024 bits

New Certificate: 2048 bits.

Any help would be much appreciated.

Thanks,

Harsh