Hi,

     I was trying to add meta-mono to yocto build, i had cloned 
meta-mono and added the layer to bblayer.conf and when i try to build 
core-image-mono using the below command, i get "No package 'gdk-x11-3.0' 
found", I have attached the error screenshot for your reference.

bitbake core-image-mono

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Thanks and Regards
Sheraz Ali Shah