I had this exact same problem on my 2001 ford escape. The mechanic told me there was a short in the seat belt connector after running a diagnostic on the electrical system.
It turns out that the problem was the electrical connection to the seat belt receiver which is under the front seat near the center console. The wires are easy to see if you look under the seat. I must have knocked the connection loose when I pushed a bunch of books under the seat and then pulled them back out.
I reconnected all the connections to be sure they were tight and the problem went away and hasn't been back since. | 
