Can't finance duplex due to 2 separate structures?

[Stephen Schoon]

Hey all, 

I'm offering on a property (in columbus oh) and my finance guy says he can't lend conventional fixed rate because  it's a non-conforming property.  It's one lot, residential, with 2 separate living structures on it.  While, I understand what he's saying, I've never heard of this being an issue before.

Was hoping for some insight. Thanks!