Administration interface dissapears

Issue Summary

Running on a drupal 6.2 install in multisite mode I have experienced some very strange behavior.

After a while, the link for the administration interface for managing block themes has disappeared from the site configuration list.

/* module install */
The module is installed in *drupal_install_folder*/modules/blocktheme as it should be for a global module.
The module is activated under all sites.

/* sites */
The sites runs in *drupal_install_folder*/sites/site_name1 and *drupal_install_folder*/sites/site_name2.

/* themes */
site_name1 runs with a custom theme.
site_name2 runs on standard themes( bluemarine, Garland )

/* blocktheme settings */
site_name1 has no blockthemes declared.
site_name2 has 2 blockthemes declared - "redblock|Red block" and "blackblock|Black block".
There are corresponding blocktheme templates defined:
blocktheme-blackblock.tpl.php
blocktheme-redblock.tpl.php

in the database for site_name2.variable I located following values:

| name | value
|----------------------------------------------------------------------
| blocktheme | a:0:{}
| blocktheme_themes | s:42:"redblock|Red block blackblock|Black block";

/* other modules enabled */
Core - Optional
---------------
Color
Comment
Database logging
Help
Menu
Path
Taxonomy
Update status
Upload

/* other modules installed */
Mail
----
SMTP Authentication support (version 6.x-1.0-beta3)

Mail API
--------
Mail API

Other
-----
Block Theme (version 6.x-1.0-beta1)
IMCE (version 6.x-1.1) (Applied "hack" in template.php to use with TinyMCE)
Nice Menus (version 6.x-1.2)
TinyMCE (version 6.x-1.1-dev with tinyMCE lib version 3.2.1) (Applied "hack" in template.php to use with IMCE)

/* what have i tried */
I have tried to change themes on both sites (also the physical files).
I have tried to swap database settings on both sites.
I have tried disabling all other modules and cleared Drupals cache

I have tried installing the blocktheme module in following ways
1) As a (for all sites) global module in *drupal_install_folder*/modules/
2) As a site shared module in *drupal_install_folder*/sites/all/modules/
3) As a site individual module in *drupal_install_folder*/sites/site_name1/modules/ and *drupal_install_folder*/sites/site_name2/modules/
#) Drupal cache flushed between installing on different places

If trying to access the administration form through /admin/settings/blocktheme I'm given a 404 - Access denied - you are not authorized to access this page.

/* what works */
When creating new/editing blocks on site_name2, the declared blockthemes are available through the selector.
When using a fresh install of a site there is no problem accessing the blocktheme administration interface.

Can anyone help me out here??