Can't extrude my first shape.

[CptanPanic]

I am trying out inventor 9, and am having some problems. I started an assembly, and created a polygon by sketching on the XY plane. I finish the sketch and try to extrude, but I get an error "[WARNING] Create Extruded Feature: problems encountered while executing this command. <FwRes.dll(416)> [r:\core\Fw\Main\FWxApp.cpp, line 3587]". If instead of an assembly I create a new part, then I can extrude a polygon. What am I missing? I thought the way to best use Inventor was to start with an assembly and creat all the parts there.
Thanks,
CP

[Orbit]

I am trying out inventor 9, and am having some problems. I started an assembly, and created a polygon by sketching on the XY plane. I finish the sketch and try to extrude, but I get an error "[WARNING] Create Extruded Feature: problems encountered while executing this command. <FwRes.dll(416)> [r:\core\Fw\Main\FWxApp.cpp, line 3587]". If instead of an assembly I create a new part, then I can extrude a polygon. What am I missing? I thought the way to best use Inventor was to start with an assembly and creat all the parts there.
Thanks,
CP

The best way to use IV. is to start on a part file. When you have your parts done, open an assembly and use place component * by right click the mouse button or the icon. Add the other parts to the assembly as above explain it than you have toapply constraints *mate, angle, tangent, insert, etc.

[Lazer]

Another best way 2 start Inventor is to open a new standard.ipt > then hit project geometry >(open origin tree) and select CENTRE POINT. now draw from the centre u projected, your models will be more stable and be fully constrained.