On page 141 the manual says
[PLEASE CHECK THAT THE LENS IS ATTACHED CORRECTLY]
• Check that the lens is attached correctly and then turn the camera off and on.
> If the message persists, contact the dealer or your nearest Service Center.
on page 14 the manual says :
This unit can use the dedicated lenses compatible with the Micro Four Thirds System lens
mount specification (Micro Four Thirds mount) such as the lens included in DMC-G1K.
Select a lens that matches the scene being recorded and your use of the pictures.
If you use a lens other than a dedicated interchangeable lens, auto focus cannot be
activated and accurate metering is not possible. Also, some functions will not work.
You should put the camera in mode manual, to avoid the error you get.
to see what lens you can use see what the manual says:
Refer to catalogs/Web pages for most current information regarding compatible lenses.
(This Site is English only.)