Problem with contributor’s logging in?

Hi guys,

I have a website with a few “contributors”. I am the admin and I have no problem with logging in to the wp-admin. In the past my writers have also had no problems and submit articles for review regularly.

However recently any user account that isn’t and admin eg. contributor/author can’t log in?

I recently installed Simple Press forum. I thought it may be to do with this even though I do think they were able to log in for a bit of time even once I had installed this.

I need the forum on the site. But I can’t make them all admins. I tried to make a new user role, but this didn’t work either since the log in still didn’t work.

Once typing in the username and password the following page shows up saying:

“That ‘something’ you are looking for isn’t here!

We’re very sorry, but that page doesn’t exist or has been moved.
Please make sure you have the right URL.”

Does anyone have any ideas? I know most of you are going to say uninstall simple press forum, but I though I would ask this first because I spent a long time customizing the forum so to uninstall it now would be quite annoying! I thought you guys may know the fix!

Thanks for your help in advance.