Very Simple dot file cannot be converted to png by Graphviz twopi - graphviz

Question

I am using graphviz twopi to generate a png file. I have many dot files but only three which cannot be converted to png. Below is one simplified example which cannot be converted:
digraph G{
overlap = false;
splines = true;
root = "a";
"a" [label ="ATCC 12633"];
"b" [label = "R M Egan",fontsize=25];
"a" -> "b" [label = "paper:1",penwidth = 4,color = black ,len=2];
"c" [fontsize=25, label = "ATCC 8014"];
"b" -> "c" [label = "paper:1"];
}
I use -v to see the details, which are:
mongodb#mongodb:/home/wuchang/newStore/allYear$ sudo twopi ATCC_12633_1977.dot -Tpng -o 77.png -v
twopi - graphviz version 2.26.3 (20100126.1600)
Activated plugin library: libgvplugin_pango.so.6
Using textlayout: textlayout:cairo
Activated plugin library: libgvplugin_neato_layout.so.6
Using layout: twopi:neato_layout
Using render: cairo:cairo
Using device: png:cairo:cairo
The plugin configuration file:
/usr/lib/graphviz/config6
was successfully loaded.
render : cairo dot fig gd map ps svg tk vml vrml xdot
layout : circo dot fdp neato nop nop1 nop2 osage patchwork sfdp twopi
textlayout : textlayout
device : canon cmap cmapx cmapx_np dot eps fig gd gd2 gif gv imap imap_np ismap jpe jpeg jpg pdf plain plain-ext png ps ps2 svg svgz tk vml vmlz vrml wbmp x11 xdot xlib
loadimage : (lib) eps gd gd2 gif jpe jpeg jpg png ps svg
fontname: "Times-Roman" resolved to: (ps:pango Times Roman,) (PangoCairoFcFont) "DejaVu Sans 14"
root = a
Rank separation = 0.000 1.000 2.000
Adjusting G using Voronoi
Node separation: add=1 (4.000000,4.000000)
I doubt it is just a bug in graphviz. My graphviz version is 2.26.3, my OS is Ubuntu 12.04.3 LTS.
Compared with a successfully-converted dot file whose convertion output is:
mongodb#mongodb:/home/wuchang/newStore/allYear$ sudo twopi ATCC_12633_1988.dot -Tpng -o 88.png -v
twopi - graphviz version 2.26.3 (20100126.1600)
Activated plugin library: libgvplugin_pango.so.6
Using textlayout: textlayout:cairo
Activated plugin library: libgvplugin_neato_layout.so.6
Using layout: twopi:neato_layout
Using render: cairo:cairo
Using device: png:cairo:cairo
The plugin configuration file:
/usr/lib/graphviz/config6
was successfully loaded.
render : cairo dot fig gd map ps svg tk vml vrml xdot
layout : circo dot fdp neato nop nop1 nop2 osage patchwork sfdp twopi
textlayout : textlayout
device : canon cmap cmapx cmapx_np dot eps fig gd gd2 gif gv imap imap_np ismap jpe jpeg jpg pdf plain plain-ext png ps ps2 svg svgz tk vml vmlz vrml wbmp x11 xdot xlib
loadimage : (lib) eps gd gd2 gif jpe jpeg jpg png ps svg
fontname: "Times New Roman Bold" resolved to: (PangoCairoFcFont) "DejaVu Sans Bold 30"
fontname: "Times-Roman" resolved to: (ps:pango Times Roman,) (PangoCairoFcFont) "DejaVu Sans 24.9990234375"
root = -290487096
Rank separation = 0.000 1.000 2.000
Adjusting G using Voronoi
Node separation: add=1 (4.000000,4.000000)
Number of iterations = 5
Number of increases = 3
Edge separation: add=1 (3.200000,3.200000)
Creating edges using splines
Using render: cairo:cairo
Using device: png:cairo:cairo
twopi: allocating a 1477K cairo image surface (907 x 417 pixels)
I tried many many modifications such as:
If I remove overlap=false, it can generate the png file but the
generated graph's node is overlapped, which doesn't meet my
requirement.
When I remove fontsize = 23 for node "c", it also
can generate the png file, but the png file is completely
wrong.

Answer 1

I'd suggest updating to a newer version of Graphviz. There has been a lot of development in the last four years. Because your verbose output ends before the number of iterations is displayed, I strongly suspect it's a bug (maybe an infinite loop) the version of Graphviz you're using.
Using 2.36.0 under OS X, your file gives me this (which is obviously not what you want):
If I comment out the line root = "a"; I get this: