[Gretl-users] Multicollinearity

Can anyone help me. I am a new user of gretl. I am doing OLS regression using multiple dummy independent variables. How do I deal with multicollinearity? Gretl refuses to calculate because of perfect collinearity. Is my approach wrong in doing multiple dummy independent variables? The equation specification that i am doing is: NAT = const + b1 Dum1 + b2 Dum2 + b3 Dum3 + b4 Dum4 where: NAT is the result of achievement tests; const is the intercept, the value of NAT if there are no project interventions; b1 is the value of NAT if there is teacher traning (dummy=1); b2 is the value of NAT if there is principal training (dummy=1); b3 is the value of NAT if there is 1:1 student to textbook ratio (dummy=1); and b4 is the value of NAT if the classroom is conducive to learning (dummy =1 if it conforms to stated classroom standards) Thanks! Clem