Still logged in problem

Hello everyone,
I have a problem with one AIX server. When I run the last command, it shows thet many users logged in on Dec 31 at 19:00 and are "still logged in".
I know that is a problem I've seen before but I don't know how to fix it. I just cleared the /var/adm/wtmp, but it started doing it again.
Anyone can help me with this issue?
Thank you.

What precisely did you type to attempt to achieve this?
How often do you start a new wtmp file? Do you ever leave it more than a year?

When was your system last rebooted?

who -b

Do these incomplete sessions appear in:

who -u

Methyl,
Thank you for your response. I cleared the file this way: cat /dev/null > wtmp
I saved a copy of the file before doing this.

When I run who -b :

system boot Dec 12 18:39

Thanks again

In the absence of the answer to the question about who -u and more questions I'm going to guess that they are coming from the utmp file. No sensible way of editing this file. A reboot clears all the odd entries in the utmp file. Do not null this file or who -u stops working !

Sorry I didn't include the results of who -u.
No, those incomplete sessions don't appear there. It is really hard to reboot this server now. I guess I'll have to wait for an opportunity to do it that doesn't affect production.
Thank you again for your help.