EViews.com

Hi
can you tell me the difference between GMM and 3sls approach. How can i estimate system GMM in eviews

I will be highly appriciate for prompt reply

i am nec in econometrics and I would like to ask sth: I run a balanced panel in Eviews 7. I have 27 countries and a time span from 1995-2010, that is a total sample of 432 observations. I imported my data and now I am trying to determine which variables i will keep in my model, however when I test for example my dependant variable with a dummy variable it gives me a sign of "near singular matrix" what does it mean?