Available UI session types: [ Qt, tcsh, csh ] Invalid MIT-MAGIC-COOKIE-1 keyqt.qpa.xcb: could not connect to display :0 qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "" even though it was found

[oktay.saglam]

I have installed everything from the beginning but this time I got “no rule to make target” message and my example didnt run. What is this ? What can I do to run the exampleB1 ?