No close button on dialog in Centos 7

Hi
I have created a dialog that runs fine on centos 6.3 but now I have imported my library into my centos 7 machine, the little close button top right has disappeared.
Any ideas as to why and how to get it back?
Thanks
Brad
I have created a dialog that runs fine on centos 6.3 but now I have imported my library into my centos 7 machine, the little close button top right has disappeared.
Any ideas as to why and how to get it back?
Thanks
Brad