Installing Sophos agent on WIndows Server 2008 Standard (fully updated)

Hi,

We just started using Sophos Central for administrating and monitoring our network infrastructure.

In our network we have one Windows Server 2008 std. edt. - fully updated til SP's and updates.

Problem: 

Whenever trying to install the server agent we get an error saying its not possible to install the agent on a Windows. 

Get this error message: C:\Users\Administrator\...\...\SophosSetup.exe is not a valid Win32 application.

(how ever, its a 64 bit installation?

Hope someone has seen this before.

Br

Kenneth