HD Extreme and LFG4

Hi everybody,
I've been doing a congress with Cat V4 in Mac Pro (2007) using and HD Extreme and a LFG4 using 1xSDI and 4x composite at same time. LFG4 has 1 input from a video mixer, 2 from 2 computers and 1 from a betacam player, Hd Extreme has an input sd-sdi from a video mixer. all inputs from LFG4 was working very fine ( no much quality but no problem), and Decklink has a little delay and lose some frames with medium quality. I was sending this signal to a Barco FLM HD18 using Extron fiber optic. Could anybody said why I has this problem with Decklink card? Input preview has very good quality but the result was not good!
Many thanks,

David