Are you using a package with Network Threat Protection feature(firewall).
Try rolling out SEP package without Network Threat Protection.

What is the version of SEP that is installed??

We are currently installing SEP 11.0.4202.75

Disable the network threat protection & see if that makes any difference?
If you disable the symantec service are you able to access the share?

Hi,

If we install SEP without "Network threat protection" we don't have the problem.

I think the problem appears  when SEP is trying to bind the filter to the network card.

 Then I would suggest deploy without Network Threat Protection. Make sure you are using updated NIc card drivers.

Which NIC are you using

Hi,

to install without Network protection is not a option.

we are using "Intel 82566DM Gigabit Network Connection"

I can now also see that we have a malfunction device, teefer2 miniport in the network adapters

teefer2 miniport is belongs to NTP of SEP
Try by uninstalling it..
For installing without NTP you have to create a package without NTP
Below doc can help you in this
Creating custom Client Installation packages in the Symantec Endpoint Protection Manager Console 

As I wrote earlier only installing AV will solve the problem, but then we will miss a lot of features.

If that is Symantec’s best solution it’s really bad.

Hmm..
As I said Earlier VPC 2005 is fully supported but VPC 2007 is not Officially supported.Since this issue lokks a bit complex and will require intense testing i would recommend to Open a Case with Symantec Support.