Login Problems @ Control Panel after installing the Forum software

I am using EE 2.9 on my localhost and have just installed the forum software that I purchased a few hours ago. Everything seemed to be simple enough and I am sure that I put all the right stuff in the correct folders. When this was done, I tried to get into the admin area to complete the installation but was unable to do so. I can bring up the admin login page ok, but after I input my details I get the error message shown in the attached GIF image. Can anyone help with this ?