Alex: Do you have "dot" installed? 

Cut-pasting from documentation: <<The callgraph image visualization ([View Callgraph]) feature relies on the presence of Graphviz "dot" utility in your path. "dot" is a utility to draw/generate an image for a directed graph. >>

Closing this as not a bug. If you have "dot" installed, but it still does not work, please feel free to reopen then bug.

I am having the same problem, with when trying to use the callgraph.php

"Error: either we can not find profile data for run_id xxxxx or the threshold 0.01 is too small or you do not have 'dot' image generation utility installed."

I do have dot installed.. dot - graphviz version 2.26.3 (20100126.1600) 

I am using Centos 5.5 (Final), kernel 2.6.18-194.8.1.el5

The problem is intermittent. If I run my cmdline php application and shut it down after a short period, I am able to view a callgraph image 

If I leave it running for > 20 seconds or so, then attempting to view the callgraph for that run, generates the dot threshold error

My application uses a constant event loop, so maybe its something to do with it constantly looping.

I am also running profiling with
xhprof_enable(XHPROF_FLAGS_CPU + XHPROF_FLAGS_MEMORY);

Thanks

I was getting this error message, and it turned out that my 
graphviz did not have support for exporting png's. You can 
check by typing "dot -T?", and checking the list of types. I 
am using CentOS, so I ended up doing a "yum install graphviz-
gd" to get png support.
The error message could be improved.

Had the same error PNG support wasn't te problem for me

Don't know what the cause is, anyway my solution was to patch function xhprof_generate_image_by_dot in 
/pecl-xhprof-0.9.2/xhprof_lib/utils/callgraph_utils.php

Function:
function xhprof_generate_image_by_dot($dot_script, $type) {
  $descriptorspec = array(
       // stdin is a pipe that the child will read from
       0 => array("pipe", "r"),
       // stdout is a pipe that the child will write to
       1 => array("pipe", "w"),
       // stderr is a file to write to
       2 => array("file", "/dev/null", "a")
       );

  $cmd = "dot -T".$type;
  
  $tmpFileName = '/tmp/'.md5($dot_script);
  
  if(file_put_contents($tmpFileName, $dot_script)){
    $output = `$cmd $tmpFileName`;   
    unset($tmpFileName);
    return $output; 
  }
  
  print "failed to shell execute cmd=\"$cmd\"\n";
  exit();
}

Referred 'dot' image generation utility is graphviz. Probably error message should be more clear.

I ran into the same error with a working well "dot" installed.

Then I found there are some non-ISO extended encoding characters in the output 
file of xhprof. 

Try use linux command "file" on your xhprof output file for determine weather 
there is a encoding issue in it.

If it's output looks like "Non-ISO extended-ASCII text, with very long lines, 
with NEL line terminators", you should do iconv in the callgraph_utils.php

eg:
$dot_script = iconv("UTF-8", "ASCII//IGNORE", $dot_script);

It works for me.

Also ensure that your php configuration does not have the 'proc_open' function 
disabled.