To turn 4 lines in a sigle entity (polyline) is required
"draw->polyline->create polyline from esisting segments"
Attached your file with all lines converted as polylines:
Chair2.dxfAbout your crash, I can't reproduce in winXP 32bits
to find a solution.
Please follow these steps:
"Start->Run" cmd.exe
cd "directory"\"with"\"draw" (like c:\Documents\MyDrawings)
c:\ProgramFiles(x86)\LibreCAD\LibreCAD.exe --debug chair.dxf 2> out.err
The previous steps open LibreCAD and load chair.dxf, then select
"draw->polyline->create polyline from esisting segments" to produce the crash
Find in "directory"\"with"\"draw" a file called "out.err" and attach it (compresed)