I cannot delete measures on SOME projects..

So.. i'm totally new to this musescore software and i m in my new project (actually the first one)
and i just cannot delete measures.. then i saw that there is this ANOTHER project that was empty but i could delete measures in it.. i was looking everywhere on internet how to delete mesure everyone was saying select measures and just press CTRL + DEL.. but nothing for me.. i was even going into the Edit settings but there was no DELETE SELECTED MEASURES as everyone was saying..
Thank you

PS sorry for my English.. its not my language..