The main site's certificate is signed by Verisign, but the socket connection for displaying the current price is served with a StartSSL certificate. Likely, the StartSSL root cert isn't trusted on your device.
but it says that the problem cert is issued by verisign
Yeah I noticed that, but I guessed maybe that the "view certificate" dialog defaulted to opening the main site cert, instead of the one that was causing the error. Not sure, but in any case you need to compare the cert fingerprint with one from a trusted computer/connection, and make sure they match.
I had the same issue on my Blackberry until I added the StartSSL CA cert to my trusted roots, and then I stopped getting errors. YMMV.