failed login puzzle

[tinkerbell]

I have used vbulletin for a number of years now but this gliche has me baffled.

I have set up a message board to be used in secondary schools (high schools). Most of the time there is no problem but if I try to take a class into the computer area to use the message board, those with accounts cant login; they get the following message:

Wrong username or password. You have used up your failed login quota! Please wait 15 minutes before trying again. Don't forget that the password is case sensitive. Forgotten your password

Even I get this message if I try and I am the owner/admin of the board. To get past this I have to get the children to register junk accounts so we can use it for the lesson, at the end of the day I clean up and delete those accounts.

The details are entered correctly and if you do make a mistake you normally have 5 attemps, this is happening on the first attempt regardless as to whether the info is correct or not.

Does anyone know why this might be happening, it only happens when a lot of people are trying to access the board (a class full ie 25 - 30) although the affects can last a while. (I still cant get in after a couple of hours, it will be ok later though)

Has anyone seen this kind of behaviour before? or does anyone have any suggestions? I odnt even know where the problem is coming from:

School connections?
my web host?
vb programming gliche?

Not the same problem as this thread https://vborg.vbsupport.ru/showthread.php?t=177126

Tinkerbell