Exchange 2010 server certificate error "error Code: 500 Internal Server Error. The signature of the certificate can not be verified. (-2146869244)"

My network environment has ISA and exchange server 2010, when I use a new certificate in my ISA and exchange CAS server and when I navigate to the OWA page form our client machine, we can get to the login page but after logging in we get an error page with the following message "Error Code: 500 Internal Server Error.  The signature of the certificate cannot be verified. (-2146869244)".

Please help me ASAP. Your cooperation will be highly appreciated.

Thanks

Babu

Babu