Applescript: file.open("r") returns empty in jsx

Question

Hey guys,
i am having a bit of a scripting problem here. The big goal for me at the moment is creating a UI script to control aerender.
To achieve getting feedback from the terminal about when an aerender process is completed, i let the terminal trigger an applescript running a jsx inside after effects (since the terminal can't run a jsx inside after effects itself).
However, this particular script needs to eval the contents of a text file that is outputted during the render process (its just a log file put into a fixed location). No matter what i do: I can't get a proper response from the script. Here is what should happen when a render is done:
function RenderEnd () {
var report = new File ("Macintosh HD/Users/macname/generallog.txt");
report.open("r");
var reportstring = report.read();
report.close();
var reportendindex = reportstring.indexOf("Total Time Elapsed:");
var reportcloseindex = reportstring.indexOf("aerender version");
var reportendstring = reportstring.substring(reportendindex, [reportcloseindex]);
var regex = /Finished composition/gi, result, indices = [];
while ( (result = regex.exec(reportstring)) ) {
    indices.push(result.index);
var ItemStringArray = new Array ();
for(var i=0; i<indices.length; i++){
    ItemStringArray.push("Finished Item " + (i+1) + ": " + reportstring.substring(indices[i]-32, [indices[i]-2]));
var AlertString = "Rendering done." + "\r" + reportendstring + "\r" + ItemStringArray.toString().replace(",","\r");
alert(AlertString);
RenderEnd ();
Running this script by itself properly returns an alert containing a message "Rendering done." plus additional info about the render time and item completion.
But whenever i have the following applescript triggering the above jsx script...
set scriptfile to (POSIX file ("/Applications/Adobe After Effects CS5.5/Scripts/AERenderEndTrigger.jsx"))
tell application "Adobe After Effects CS5.5"
  DoScriptFile scriptfile
end tell
...the line report.open("r") just returns empty.
Same goes when i place the jsx in the startup folder and just call the function RenderEnd () via applescript. It's as if the file open/read stuff does not work when using applescript.
Does anybody have an idea about this or knows the reason for why this obviously wrong behaviour happens? Maybe someone knows a different approach of how to get feedback from a completed aerender process back into a UI script.

Answer 1

Ok, i finally found the issue:
Applescript apparently does not recognize file paths beginning with a drive designation:
When i change the file path part of the report file from
var report = new File ("Macintosh HD/Users/macname/generallog.txt");
to simply
var report = new File ("/Users/macname/generallog.txt");
everything works as it should.
It's still a bit weird and i don't understand this. Maybe someone can explain this to me, please?