Some customers cant reset their password

I dont know if anybody else has experienced this but some of my customers when they come back and need to get a new password are unable to log in with the password they get sent.
Even with cut and paste it wont work for them.
Then it seems if they try again the next day it will.
If they send that new password to me I can log into their account no problems.
Is this a cookies or cache issue on their machine? I have never had this issue myself so cant test how to fix it.
just want to be able to tell my customers something useful.

Thanks in advance

What version of Zen Cart are you using? What browser are the customers using?

Im on version 1.3.9d. I dont know what browser they are using.
Ill ask a few customers and get back to you.

I also have an issue where some of my clients create a link to my site that is an open session. I try to stop this but now and then it happens.
This causes customers to mixed shopping carts with other users orders cos they are both on the same session.
Is there someting in sessions I can change to stop this.
Somebody has suggested "is it possible to remove the URL-based sessions and use cookie-based sessions instead?"

Ok so Ive just tried to log in as a customer using Internet Explorer 9.
I type in my username and password and it refreshes the page but is back at the login screen as if I have done nothing.
If I type the wrong password it recognizes this and gives me the appropriate error.
I then type the right password and again it does not log me in and just refreshes.
Is there any FIX?

I am having the same problem with 1.5.0 except the "customer" is me--I created a login so I could test buying things and it worked until today--now it won't let me login and I've done the "forgot password" thing twice, yet it won't let me in with those either--it just reloads the login page (with the create account stuff underneath)... what is wrong?

I cleared my cache and cookies and it started working.

Does anyone know a fix to this as I get this same problem even if I use a new browser to log on. So nothing to do with the cache. However, after several times of trying suddenly it just starts to work.