Client Authentication Certificate error pop-ups when accessing https website via Safari Web Browser but not via Internet Explorer or FireFox

We are a Payment Gateway and have been experiencing issues where for some weird reason when our clients try to effect a payment via our Client Login Payment Console URL accessible to the Public (as an example: https://www.itaintworkingatall.com/console/login.cfm) via the Safari Web Browser they get a message to select a Client Authentication Certificate. We can not resolve this problem despite searching all the forums for a solution. I even contacted GeoTrust, they tested our SSL integrity via the GeoTrust SSL Checker and all seems well. They went on to try the link and I also tried the link via Safari Web browsr and get the same Client Authentication Error. The SSL Certificate is an Extended Validation SSL bond to our website's Virtual Directory via IIS 7 (in this case as an example - www.itaintworkingatall.com IIS 7 Site). The Server running IIS 7 is Windows Server 2008 Datacenter R2 (64 Bit). If our clients use or I use Internet Explorer or FireFox as a browser to access the same Client Login Payment Console URL (in this case as an example - https://www.itaintworkingatall.com/console/login.cfm) on the same computer they or I do not experience this problem, I can access the page and effect payments successfully. Please can someone kindly assist? Thank you