Connection problem to server

First the setup of the system. We had one server which acted as a DC and also
run some web application. Now we have installed a new server (2008), demoted
the old one and made the new one as the DC, AD, DNS, File, DHCP and the old
one is only running the web application.

I have joined all workstations to the new domain which was no problem at
all. The problem however is that if I want to access the files on the server
(Network Place, Entire Network, MS Windows Network, XXX Server) I can see
the server name, however, I cannot connect to it. It says no permission!
However, strange enough, if I do a search for the IP of the server I can
connect no problem, no login screen or anything shows, just everything seems
normal. I can Map the drive and it works even after reboot, etc. Another
symtom is that I can ping the server from any workstation, however, I cannot
ping the workstations from the server. It very much sounds like a DNS
problem, however, nothing wrong I can see there. I cannot post a IPConfig as
I am not at the customers site however it is:
Server
IP Address 192.168.9.1
Subnet: 255.255.255.0
Gateway: 192.168.9.3 (Firewall)

Prim. DNS 192.168.9.1
Alter DNS 192.168.9.3

Workstations
IP Address 192.168.9.61.......
Subnet: 255.255.255.0
Gateway: 192.168.9.3 (Firewall)

Prim. DNS 192.168.9.1
Alter DNS 192.168.9.3

Windows Firewall is disabled and there is no third party firewall installed.
Anyone has any idea? It is driving me crazy.

Thanks to all you guys out there.