Unable to create solid or loft surface

I am a newbie in microstation 3D . I am attaching a dgn file that I am trying to make a into a  solid.

I used  two method.

first I use convert to solid but it failed.- got a message "unable to convert to solid " which is not useful message.

I tried a few methods . I selected all the surfaces and also leave boths ends unselected. both failed. 

2) I tried to use loft  surface using guide edges. I get a message unable to perform operation.

Can some expert tell me what is wrong ?

download here : www.dropbox.com/.../3DComplex%20Curved_slab1.dgn