My iPhone 4 will not allow me to access a secure web site anymore

I use a web based application in my work that has a mobile application. I have been using it for months and now, when I attempt to log in through the site, it will not allow me to. I can't load the app shortcut, I have cleared the history, stopped the applications in the background, everything that the web based application provider has told me. I can easily access it on my wife's iPhone 4 and my daughter's iPhone 4. We all are running the update iOS 5.0.1 and I have backed up, rebooted, re-synced, etc. Can anyone help?