User level not recognized after merging user tables

Hi all,

Even though I have no PHP knowledge whatsoever, I decided to merge the user tables of Invision Power Board and WordPress recently. I did so by expanding the IPB table a bit and changing the .php files of WordPress to refer to the proper table and columns.

Now I got all users to show up on my WordPress administration panel, but for some reason the user levels aren’t working properly. I can change the values in the database itself and they will show up in the admin panel, but they aren’t changeable from that panel itself (i.e. by promotion).

But the worst thing is that trying to write a post makes an error message come up:

Since youa€?re a newcomer, youa€?ll have to wait for an admin to raise your level to 1, in order to be authorized to post.
You can also e-mail the admin to ask for a promotion.
When youa€?re promoted, just reload this page and youa€?ll be able to blog. ??

I can log in as an author (user level 8) or as the admin (user level 10) and still get this message. So for some reason, the user level isn’t being validated properly. I’ve tried to scan all the files, but I don’t understand the code well enough to see where the problem lies.

Can someone tell me what files are necessary for this validation, or what parts are likely to cause the conflict? Thanks in advance.

Edit: I am using WP 1.5