The lm_custom table was removed for v1.8. The update processes the entries and moves them to new tables, lm_chtml and lm_chtmld.
This was the tricker. After I uploaded all the files form v1.8 I started ListMail for the first time. But I didn't realise it was upgrading en I stoped this process. I think the script finished half. The next time I started ListMail the script start updating. But some parts of updating where allready finished. For example the table lm_custom was removed.
To solve this problem I have removed all 'or die( )' parts from the update.php file en let the updating script begin. Of course there were a lot of mysql errors, but I think it's upgraded now. I have tested and it looks like the script is working correctly.
I wil be more careful the next upgrade. Maybe I will start the next upgrade with a fresh installation.
Maybe you should remove the login box when updating is in progress. In that case, people like me, will see that something different hapens.
Thanks for all your help. This script and all your support is really great.