Problem with simple GARCH estimation in Eviews6

[simon_kam]

Dear All,

I am running several estimations of GARCH models on financial returns using a simple syntax:

equation equation name.arch(garch) y

In a few cases I obtain a negative ARCH factor, and a GARCH factor above 1. Anybody knows how to "force" both factors to be between 0 and 1?

I would be grateful for any helpful answers.

Cheers,
Simon