Spotlight comments not available?

Question

I've developed an internal website at work that uses PHP, MySQL, Applescript and PDF files to manage the workflow for print projects.
The basic setup is that a user "publishes" a PDF from InDesign using an Applescript (which ensures the PDF is created with standard settings and file security) and the PDF is copied to the webserver into a folder for review. The applescript then puts the designer's name into the PDF's Spotlight comments.
Someone reviews the project from a web-page, which looks in the folder and displays thumbnails of its contents. PHP runs an exec() to get the Spotlight comments, and displays the designer's name below the thumbnail, along with the date and time the PDF was "published".
$PDFcomment = exec("osascript -e 'tell app \"Finder\" to get comment of POSIX file \"$projectsFile/$shortID/$dirShort.pdf\"'");
The problem I'm running into is that this command is not consistently returning the Spotlight comment. Often the PHP webpage says it's empty, but when I go to the networked volume where these PDFs are stored and Get Info, I can see the correct comment.
The comment will only appear if I use the Finder on the machine that houses the PDF and Get Info. Subsequent viewings of the PHP webpage then return the correct comment.
How can I force the Finder to get the current Spotlight comment without having to manually check the file first?
PowerMac G4   Mac OS X (10.4.5)  

Answer 1

Running the password reset actually recreated the problem but that's ok because it helped lead me to the true cause and answer. Being a member of the wrong group can cause all sorts of annoying problems e.g. asking for authentication when deleting files, spotlight not indexing some files etc. Luckily this post http://www.macosxhints.com/article.php?story=200711291134001 had the answer. I'll sum it up here:
I had a problem with spotlight not indexing some files especially spotlight comments. I'd tried deleting spotlight-V100 to re-index and many other things which did not work when all along it was a group membership problem.
I had upgraded from Tiger to Leopard. The GUI tools in Leopard showed my primary group was staff and nothing looked wrong until I discovered the Unix commands thanks to your great script. I didn't run the script but it was very well commented so I knew what the commands did if I ran them in terminal.
dscl . read /Groups/staff
showed I wasn't in the group staff. (even though system preferences>accounts>advanced options said i was!)
sudo dscl . append /Groups/staff GroupMembership $USER
added me to group staff.
sudo chgrp -R staff $HOME
changes group ownership on all files in home to staff.
sudo diskutil repairPermissions /
repair disk permissions.
Reboot.