Problem with capturing a TV post (Marvel G400)

[GunX]

On some channels I got this error "Can't capture video : The video is unstable or video is not correctly set" although the video and audio are just perfect, the image seems very good, no problems like flickering or any stripes...why is that, what can I do ?
I got the PAL version and the channel is TV5.... I tried setting the video standard at PAL, SECAM or NTSC, but still nothing ... audio both AM or NICAM standard are useless.... what can I do ??

Very frustrating indeed...