One of my character is having a problem

One of my character, out of 6, cannot move the different screens around. I put my mouse on the edge of the screen to move it, and no X arrow shows.
All my other players have no problems moving any of the screen around the window. All on the same computer, same Leafcull world.
I also have a post in the tech board. But no one is answering. Does anyone have an idea of why, just one guy ? Thats so strange:(
Thanks.