when I connect the mechanism to the Panasonic Gt 20 this can´t detect it. Any idea?
can you give us a bit more of information. How are you connecting the device to you TV? Have you tried in another TV set?
I have solved by connecting the WD in the composite and setting panasonic video playback automatically, then reconnected in hdmi.
This is a known issue for Panasonic owners, you only have to search for it and there are a lot of users in other forums with this issue (at least owners of Panasonic PXXG20 model). WD Elements Play connected to a Panasonic G20 via HDMI will result in a black screen; the TV seems to detect that something is connected to the HDMI port but it cannot display the image. As someone commented, it is solved if you enable automatic playback (which is, IMHO, a really crappy solution).
Should be nice if WD could investigate this, there are a lot of Panasonic users out there. Some more firmwares are really needed for the Elements Play.