User Access Control - I Need Some Expert Help

Hello, All -

A few months ago I was working on a project which required another layer of admin control over the users. I had to find a simple way to control the categories into which the users could post their records. I figured the easiest solution would be to create a drop-down menu in the User Accounts editor which listed all of the categories on the site. I could then select which categories each user was allowed to access.

When the user came to post a record, the category menu on the record screen would list only those categories I had hi-lighted.

Simple.

Except it didn't quite work!

I created the (multi-select) drop-down menu in the User Access editor - called categoryAccess.

I then created a category menu in the Record editor and added the following (advanced query) code:

<?php
$categoryAccess = join( ",", explode( "\t", trim( $CURRENT_USER['categoryAccess'], "\t" ) ) );
?>
SELECT num, name
FROM `<?php echo $TABLE_PREFIX;?>category`
WHERE num
IN (<?php echo $categoryAccess;?>)
GROUP BY num

It does work - but not all the time - and when it fails it throws an SQL error. Crucially, this error is seen in the backend and on the frontend pages of the site.

This should be realy simple way to control user access on the site - but I can't work out why it doesn't work properly.

I'd be very grateful for any support.

:o/

Perch