User couldn't log in now I can't log in

I have used zencart for a long time without fail

the owner of the site i manage called me and said a customer reset her password and now couldn't log in

so i look in db and all seems fine, there is a passwor etc

so i tried to login

I get a message

ERROR_SECURITY_ERROR

I can't even login with the email and password i have had since i set up the site

so then i tried to recover my password

what could be going on

now just recieved the email

and tried the new passowrd

still get security error

Make sure that you are not sitting on a browser window for a long, long time before trying to login again ...

The security error is usually the result of being on one session id then logging in with another which will fail and you will need to login again ...

If you are seeing:
ERROR_SECURITY_ERROR

instead of:
There was a security error when trying to login.

it sounds like you have missing or out of date files ...