Could be many things. Check that you are not trying to scale a selection of some sort Use Select -> None and Scale tool in Layer Mode (left side icon)
Other than that: post a screenshot somewhere showing the problem + the layers + the scale tool settings
eg: https://i.imgur.com/04LelEM.jpg
Other than that: post a screenshot somewhere showing the problem + the layers + the scale tool settings
eg: https://i.imgur.com/04LelEM.jpg