dummy variable in panel data

[mahan]

hi,
i'm using panel data for 3 cross section and 11 years. i use one variable that is fixed for all cross sections but i see near singular matrix!!! why?
and, how i can use dummy variable in model? how i can exclude one year?
thanks for any help

[startz]

You can't have cross-section dummies and a variable that is constant within a cross-section.

Use the smpl command to choose years.