Check your input units.
I use sketches from AutoCAD. I start a sketch in IV then use the Insert
AutoCAD file button. With IV6, the lines do not turn "black" to show they
are fully constrained. Is this a known problem? I have had to open the
.dwg of the sketch into an .idw, then copy and paste into the .ipt sketch.
It works but is a MAJOR pain.