[Solved] Seemingly Random Banning

I've recently been getting the following error when trying to access my [url=http]site[/url]:
It appears you have been banned from this website. If this is a mistake or you are not sure why you are banned, please contact the board administrator.
Board Administrator: *my email address is here*
You have been banned from this site.
The error appears on a white page. So far I have only noticed this when using Internet Explorer. However, I can usually just close the browser and reload the site and not get the banned message. I, as admin, as well as both registered members and guests have also gotten banned. Testing in FireFox I have yet to get the banned message.
Searching the forums I found references to a user -1 in the banlist so I checked that but did not find -1 there. Also there is a post about the referrer banlist being limited to 255 characters and exceeding that causes a similar but slightly different banned message. Would this be the same list as seen as "Un-ban one or more IP addresses" in the ACP's Ban Control? Not sure if I should just try deleting a bunch of the ips listed. I also checked to make sure I have the correct number of admins and mods set.
I know I need to update to phpBB 2.0.23 which I will try next but anyone have an idea what might be causing this? Is it simply a cookie issue? Any help would be much appreciated <img>
Edit: Hmm, did I enter this post incorrectly? I entered all the information in the CBACK Supportticket System but I don't see it now.
My host recently upgraded to php 5.1.4 and I didn't notice this problem before that.
It appears you have been banned from this website. If this is a mistake or you are not sure why you are banned, please contact the board administrator.
Board Administrator: *my email address is here*
You have been banned from this site.
The error appears on a white page. So far I have only noticed this when using Internet Explorer. However, I can usually just close the browser and reload the site and not get the banned message. I, as admin, as well as both registered members and guests have also gotten banned. Testing in FireFox I have yet to get the banned message.
Searching the forums I found references to a user -1 in the banlist so I checked that but did not find -1 there. Also there is a post about the referrer banlist being limited to 255 characters and exceeding that causes a similar but slightly different banned message. Would this be the same list as seen as "Un-ban one or more IP addresses" in the ACP's Ban Control? Not sure if I should just try deleting a bunch of the ips listed. I also checked to make sure I have the correct number of admins and mods set.
I know I need to update to phpBB 2.0.23 which I will try next but anyone have an idea what might be causing this? Is it simply a cookie issue? Any help would be much appreciated <img>
Edit: Hmm, did I enter this post incorrectly? I entered all the information in the CBACK Supportticket System but I don't see it now.
My host recently upgraded to php 5.1.4 and I didn't notice this problem before that.