When i try to add gmail-plasmoid i get message :
"This object could not be created for the following reason:
Script initialization failed"
Sorry but i couldn't find other usefull information in logs etc. about this problem
any ideas

you have to install python qt package and maybe python plasma

I've installed both plasma-qt and plasma-scriptengine-python but still get the can't initialize error.

Could someone please confirm if adding the two packages worked for them. thanks.

The GMail plasmoid could possibly be a Google Gadget. I do not know if Kubuntu provides support for them in it's Plasma packages however.