Spline from lines

Hi,

I scanned an object on or  CNC CMM machine, from the scan I get an .iges file.

The iges file contains the curve that I scanned but its divided in lines.

When I use the command 'smooth curve string' some of the lines are not selected and I get an error 'selected section curves include branches'.

Anyone an idea what I'm doing wrong?

I want to create a spline from the lines and then use the command "smooth spline" to get get a smooth curve that I can use.