The errors may indicate some problem with the basic feature geomery that is causing the turn editing to fail. Perhaps you can run the GP tools: Check Geometry and Repair Geometry to see if that will identify/fix such problems. Make sure to keep a copy of your data as you do these things.
Also, are you able to run build network successfully? If yes, take a look at the log files (they go to %TEMP% folder), namely Build.txt and BuildErrors.txt to see if any problems are being reported there.
Jay Sandhu