Hello Bernhard

At first when I saw your screenshot I thought that rail curve was one continous curve, but close inspection yields you have your two rails and the profiles, all connected.

I did notice all your curves where having diferent spans, I rebuild them all to cope with the pointers I told you in the other thread (Opossing curves need to have the same spans remember?) and yet again it did not compute the results.

So I think the only solution as of now for your predicament is to birail the surfaces one by one. That´s the way I obtained the surface you see in the screenshot. To achieve it instead of going around picking all the profiles, just pick two profile curves and then the rail ones, and on and on. You can also use Birail2 for this.

Resulting surface is not a very pretty one, but you could rebuild and stitch afterwards.

On a little side note: You wouldn´t even imagine how many resources that big ass grid of yours is eating mate. Stop fiddling with the preferences and viewports. Almost crashed my machine.

Hope this helps,