I have had similar issues with Windows 7. Apparently, Usmleworld told me to get rid of 1.7 and get 1.6 for windows 7, but in like of all the security issues with Java 1.7 versions and below, I got rid of everything Java related on my computer.
My only personal access is my ipod touch through the usmleworld app. I am pretty sure ipad works too.
Ultimately, Usmleworld needs to provide their customer base their Qbank not using Java as an "intermediary." I am pretty sure Kaplan doesn't have this issue. Please request Usmleworld to provide us their Qbank not using Java like I have. And ask them as soon as possible in regards to your test date.
FYI I downloaded 1.6 to see if the questions would pull up on my Windows 7; it didn't work either. Of course, I got rid of everything Java related due to the U.S. Department of Homeland Security warning.