Please help me Login error

[thienlongtelecom]

I convert my forum from PHPBB --> VBB 3.5.1 and after that upgrade it to VBB 3.5.2
It run ok and mamber can login ok.
But in some day alots member say that can not login and have 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? Click here!

I go to admincp and reset password for my member and in my computer I can login ok.

But if my member login qith that pass and user name in they computer it will have that message too. I don't known why ???
Please help me verry urgent my member will hate my forum if this problem more and more.

This is my forum http://www.thienlong.org/forumvn

best regards

[Floris]

I'd email all your members with the request to reset their password, so a new one is set and they have a new one on record. This will avoid having them try more then 5 times.

[thienlongtelecom]

Can you explant more detail ?
I can not fix this error too.
Alots member ask me about this.
Please please