What is the output of "apt-cache policy xlibmesa-gl-dev" and also "apt-cache policy xlibmesa-glu-dev" ? You can run this in the terminal (applications -> accessories - > terminal)
Do you have any unofficial repositories enabled?
What is the output of "apt-cache policy xlibmesa-gl-dev" and also "apt-cache policy xlibmesa-glu-dev" ? You can run this in the terminal (applications -> accessories - > terminal)
Do you have any unofficial repositories enabled?