My system has a Decklink Extreme and a Parhelia card and I have not experienced any problems. Have you tried running the latest Matrox drivers for the Parhelia? Also, have you tried using a different PCI slot for the Decklink? Maybe your motherboard is having a resource conflict between the Decklink and Parhelia. Just a thought.
Good luck.
MB – Supermicro P4SCT+II
CPU – P4 3.4
RAM – 2GB
OS – Win XP SP2
Video – Matrox Parhelia with dual LCD monitors
Boot HDD – WD 7200 RPM
Video array – Stripe set of 4 x 250 GB SATA HDD with Promise FastTrak S150 SX4 RAID controller
Video Capture – Decklink Extreme v4.8.1
Video Editor – Adobe Premiere v1.5
Jeff Anderson