If you're using the "Tile Map" object, it's possible that you have a Tile Map on the game layer, but you don't have a Tile Map on the background layer.
You'll need a Tile Map object on both layers, if you want to draw tiles on each layer using the Tile Map drawing tools.
In order to specify which Tile Map object you want to draw on, you can select it before drawing.
While the Tile Map editing panel is open, if you want to select things you'll need to switch to the normal selection tool (arrow pointer), which you can choose from the Tile Map editing panel's toolbar.
Notice that the top of the Tile Map editing panel will show the name and UID number of the currently selected Tile Map object.
Finally, you can hide a layer by clicking the check box beside it's name, to double check that you're drawing on the correct layer.
Hope that helps.