we want to to convert an quicktime ( animation codec, no audio)

into the following:

Final Delivery Video Format & Illustrations
- MPEG2, 1920x1080px
- 50p
- I-Frame only
- HP@HI
- CBR
- CBR
- 40Mbit
- Closed GOP
- GOP<15
No audio is required for these animations


So far we keep getting this error:
MPEG2 encoder: Invalid video horizontal size(1920)/vertical size (1080)/frame rate(50.00 fps) combination.

if i convert it with 25fps it works fine but not with 50fps?

Can anyone help?