Thanks for your help. You pointed me in the right direction. It was a reference file. I found I could measure along element after going to File/Reference and turning Locate on.
I'm brand new to microstation and I'm stuck !
I was using 'measure along element' sucessfully, but now I've got a file and when I try to do it I can't select anything and a 'no entry' type sign shows up. Can anyone help ???