Cannot resolve KeyInfo for unwrapping key: KeyInfo 'SecurityKeyIdentifier
IsReadOnly = False,
Count = 1,
Clause = X509IssuerSerialKeyIdentifierClause(Issuer = 'CN=MyCert', Serial = '-903515464456238801534567116928')
', available tokens 'SecurityTokenResolver
TokenCount = 0,
This error usually means that the server had digitally signed its response using an unexpected certificate. The expected certificate is the one which the client has configured as the server certificate and have possibly used to encrypt the message with.
So as with many of the security interoperability problems, you should verify that you use the correct certificate on both sides of the wire.