WellI havent made the apache tut myself yet, but for this I thought I would try to recreate it.

Pic one
Shows roughly the same shape, just without the all important details.

Pic two
This shows a zoomed in view under xray of the column area. To create it i just extruded a couple of faces upwards. The top section (green) was my control and left as normal, while the bottom section (red) i purposly put in extra faces (circled) by extruding the red edge.

Pic three
This shows what happened when i Extruded the faces backwards as you tried to do. The top green section worked well and as expected, while the red section came up with the exact error you seem to be having.

So what Im trying to say is, have you looked in Xray at your model at a similar view as Pic 2, to make sure that you dont have any extra geometry / faces inside your model?

I hope some of this helps and solves your problem, if it does - Great! if it doesnt let us know so we can have another go at it!