website request error on cname forwarder

Hello experts,
i have the following scenario:
we have a new website which can be accessed across the WAN at . is pointing to .
On the LAN site we have a ActiveDirectory domain xyz.local and a manually created DNS zone called cause we use some internal services for that . In addition I have created an A record on the DNS server for I have also created a CNAME alias that is forwarded to the A record .

Now to the problem:
Some user from the LAN cant open the website or  In Firefox nothing happens and the IE shows the message "The page can not be displayed" .
From the WAN the website works perfectly.
So there must be something in the LAN. I can exclude the DNS server because it works on some computers.

Whatelse can i check to fix this issue?

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I think you discard the DNS server as a problem too soon.

Please still do a nslookup on the problem PC's?
deibelAuthor Commented:
Server:  UnKnown
Address:  ::1

Address: (changed)
On the problem PC, use WIreshark to capture the whole port 80 conversation.
deibelAuthor Commented:
i have installed wireshark and start to capture but but unfortunately, I dont know how to evaluate the wireshark results. what should i look after?
First of all, quite as many programs as possible.
Start the browser, input the URL, but do not press enter yet.
Fire up Wireshark, select the correct  network interface, press Capture Options, in the Capture Filter, fill in
port 80 or port 53
Click Start
Now in the browser, press enter. Wait a few second for the error.
If there isn't a privacy issue, you can now save the captured data and attach it here.
If not, try to evaluate the packets yourself, mostly using right mouse click, Show TCP Stream. Then look at the commands.
Also look the the DNS requests, what's happening there, who does the PC talk to for this info.

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