Some end users not seeing the Next button in a quiz

A bit of background to begin with, so that you can understand the constraints we are have in finding the solution - we are an e-learning company which runs an outsourced learning management service for a large corporate.  The corporate was recently bought out by an international company, and the international company has provided a lot of  published Articulate material to be put on the corporate's LMS.  As a result, we don't even know what version of the software was used to develop the material.  We are also unable to change any of the content, unfortunately, and are unable to request that any of it be re-published by the original developers either. (And I'm not allowed to provide any screenshots either, I'm afraid.)

We are having trouble with the quizzes whereby a small number of users are unable to see the next button at the bottom - the quizzes are set up with an introductory page with instructions and a next button at the bottom.  Once a user presses next, the quiz begins and this button is replaced by the submit button.  Most of our users have no trouble with this, but a few cannot see the next button at all.  We think this might be down to PC settings, but haven't been able to come up with a solution other than trying a different browser, which doesn't fit with their company IT policy.  

The latest person to have this problem has a recent version of flash player (they say version 12) and is using IE8.  (This is common at that corporate, and people who don't have this problem have the same versions).  We've cleared the browser cache as well, and made sure that the LMS is a trusted site.  Does anyone have any other ideas of a setting we might need to change or try?