Sorry for not getting back in contact sooner. Are your players using phones or tablets? If they are using tablets, can you have them post bug reports in the bug and technical forum so we can help them solve this issue? If they are using phones, phones are not officially supported.
Hi Ciaran K. - Also for clarification, are your players attempting to use roll20.net from their web browser on their tablets or attempting to use the Roll20 App which is available in the app store?
The Table on Tablet support listed on the supporter page is referring to using roll20.net on tablets from the web browser - this should work for your users now with no issues, assuming you are the one who originally created the game. Roll20 for iPad and Android is a different free-to-use mobile tablet application that should be compatible with Android 4.4 or higher on Tablets 7 inches or larger & iOS 6.0 for Apple products on a 7" or larger tablet. If they are unable to download Roll20 for iPad or Android - then that means it is not compatible with their devices. Please have your players try the site on their web browsers on their tablets - if they can get into your game then it is working as intended. As for the app - if they want to jump in this thread and give us the specification for their tablets we can look into it.