Lower triangle BV Bekk-Garch

[nicktz]

Hi guys!

I am trying to fit a lower triangular form to the Bivariate Bekk-Garch in mean model. I attach the coding and the data. Please help..
In it I try to make the Alpha and Beta matrices lower triangular to limit the direction of volatility spillover from y2-->y1.
Please could you check my code if its right (or have any suggestions) and help me spot a mistake as it is not solving - it says "missing values in Logl".

I am struggling to find the problem! Thanks a lot!!

N