I am facing this message :

Could not get tag data from tables expertise_tags and expertise_links

Both table expertise_tags and expertise_links exists

The modifications, remarks 

made are fine, but in Line 676, 770, 792, 812  and 822 it looks that there are problems with the foreach statement and Array. I'm not so experienced with changing it to a  while statement, that's what I have found out could help.

Here are the error message when updating tags

Around here (I'd give a line number but mine are out of sync because I had to make it play nice with the invitations mod):

// find the users who have been tagged with it

You need to insert the DB prefix in the query like so:

FROM ". EXPERTISE_LINKS_TABLE ." l, ".$db->prefix."users u

As you do around here:

// get current tagging users data for this user, if any

Replace query with:

$sql = "SELECT DISTINCT u.id, u.username FROM ".$db->prefix."users u, ". EXPERTISE_LINKS_TABLE ." l

Otherwise, this pretty much doesn't work if you use a DB prefix for your forum.

I'm not sure why, but in the transfer screen after adding a tag there is the following error:

Also for anyone with Tobi's invitations mod, edit expertise.php:

Find:

define('PUN_ROOT', './');
require PUN_ROOT.'include/common.php';
require PUN_ROOT.'expertise_include.php';
require PUN_ROOT.'lang/'.$pun_user['language'].'/expertise_lang.php';
require PUN_ROOT.'lang/'.$pun_user['language'].'/profile.php';

After, add:

require PUN_ROOT.'lang/'.$pun_user['language'].'/invitation.php';

Also, some suggestions:
- Make already confirmed tags viewable in the profile, then have a link just to add them
- Let guests view confirmed tags
Like you said in the notes:
- Some kind of notification when you have new tags waiting
- Administrator button to remove unused tags from the database
And some picky OCD things:
- Move expertise_include.php to /include
- Rename expertise_lang.php to just expertise.php
(Those don't really matter but they bug me)

Otherwise, great mod, thanks for making it. It looks like you put a lot of effort into it.

Project: http://punres.org/desc.php?pid=133
Download and Screenshots: http://punres.org/files.php?pid=133

PunRes Discussion: http://punres.org/viewtopic.php?id=925