Map Background not showing for players

So Tonight I was GMing for the first time using Roll20 and we started doing Lost Mines of Phandelver. I bought the pack however when I got to the Cragmaw hideout the map was not showing at all for the players. All they could see were tokens and a random rock I placed there.  I have fudged with the layers as It was a pre purchased pack and didnt want to stuff up the settings. Any Ideas would help. Thanks

Is dynamic lighting on for the page? Do the PC tokens have sight? Is there a light source (or global illumination on the page)?

Was the map accidentally moved to the GM layer?

Can you provide a screenshot so we know more about what is happening then we can proceed from there with more information.

I went through all the suggestion and yes for some reason the map was on the GM layer.... Not sure how, but tis a silly mistake that I over looked. Should be all fixed now hopefully. Thanks for the replies, hopefully next session will go without a hitch. 

It's happened to others. :)