Help with error on customers logging into account on opencart

When customers return to the site to log in they all get the same error "warning- no match for username and or password "
I've tried using the auto approve and also the approve nothing makes any difference,
I've also added an account myself and I'm having the same issue, I can log in and out of the admin area without issue it's just the returning customers that get this error
Any help would be great
Site is realtrackmodels.co.uk
Thanks

You haven't listed:

1. Your OpenCart version?
2. What extensions you're using?

I'm using version 2.0.3.1 the latest version
With echo theme
No extensions

hi,
most probably your config.php file is changed.
try to check if database name is same that you want to use.

Thanks, I checked the config.php file and it was using the correct database

But it seems to be a random problem, you can log in then you can't, then you can then you can't again, it's all very odd....

There is a problem with your config or htaccess.
It shows as the fontawesome icons not rendering because your SSL is not configured correctly.
There are numerous threads on this on these forums.