First, in some cases, the issue is related to a bad time and date setting on your computer.. Check to make sure your computer time and date are correct.. If not, fix them and if necessary, replace your CMOS battery to keep the date correct.
Next, see the link below to make sure the server certificate is up to date and installed on your computer. (It may have changed.) Generally, contacting the server's IT folks will allow you to get this fixed quickly.
Hope this helps.
I used to be able to conect to my office email from my home computer but I now get an error message code 20 that mentions something about a "proxy server". Is there a fix within Microsoft 2007, itself, that can fix this? Or do I have to purchase one of the MANY registry repair programs?