some customers cant complete checkout HELP!

[modchipfitters.co.uk]

please can sonmeone help me
i have a store that has been running for about 3 months now and in generalk it is doing very well

but it a few customers have reported that they cant get to the end of the checkout
they get as far asd checkout shipping and then to continue to next step button is completly missing and so they cant reach the payment screen

i have tried from my end and cant get this problem to happen
i have even had customers ring me and give me thier login details and i have put the order through on my pc perfectly ok
but there has been about 12 people that have told me about this so god knows how many it has happened to that hasnt let me know

i am running zen 1.3.5
i have tried using css buttons and also images for buttons but th8is makes no difference

has anyone got any idea's what might eb the problem?

[Kim]

When you have a situation like that, you need to ask the customer what browser and OS they are using. With out those pieces of information it is near impossible to determine the problem or to replicate.

[modchipfitters.co.uk]

When you have a situation like that, you need to ask the customer what browser and OS they are using. With out those pieces of information it is near impossible to determine the problem or to replicate.

we have asked the customers what browser they are using and it is alwasys a different answer

i have tried with firefox both version 1.5 and v2
and also with ie 6 and 7 both 32 and 64bit editions

for the os i have tried win xp, win x64 and windows vista and have not been able to replicate the problem

[Merlinpa1969]

find out if they are using AOHELL

[modchipfitters.co.uk]

dont think so because i have been watchng some of them in who's onoline and there doesnt seem to be any particular isp involved

[Kim]

Then also ask if they have javascript disabled or cookies blocked.

[modchipfitters.co.uk]

well still cant find ther problem
1 thing i have noticed is that when a customer gets stuck the page info from who's onlinecomes up like this:
/index.php?main_page=checkout_shipping&zenid=d510f938bae276c10b28fc87f7a7a32c

and yet most customers that havent had any problems just have the following:
/index.php?main_page=checkout_shipping

does this give anyone any idea's?

[Kim]

What are your sessions settings?

[modchipfitters.co.uk]

What are your sessions settings?

Session Directory /home/modchip/public_html/cache
Cookie Domain True
Force Cookie Use False
Check SSL Session ID False
Check User Agent False
Check IP Address False
Prevent Spider Sessions True
Recreate Session False
IP to Host Conversion Status true

[modchipfitters.co.uk]

Session Directory /home/modchip/public_html/cache
Cookie Domain True
Force Cookie Use False
Check SSL Session ID False
Check User Agent False
Check IP Address False
Prevent Spider Sessions True
Recreate Session False
IP to Host Conversion Status true

are these settings correct?