Overlaying an Exchange Calendar in Sharepoint 2010 trust error

Hi

I am attempting to overlay an Exchange calendar over a sharepoint calendar and am getting the following error

Could not establish trust relationship for the SSL/TLS secure channel with authority '"my exchange server"'. (eeb00c40-a6d0-42f8-8afb-96735fbd3d0e)

I have entered the correct exchange server EWS where i have replaced it with "my exchnage server".

Thanks in advance, all help appreciated