@vouzou81,
Without going into the specifics of your model, it is possible that two variables that are listed as independent are highly correlated, so when you dump them into a statistics program, one will flag as not significant. For example, if I plotted family wealth versus my age and my wife's age, there is a strong correlation with either, but since our ages are perfectly correlated, a stats package will say one is significant and the other is not if you combine them.