"Network error" means just that: its not a problem with the server keys nor the credentials. Nor is it failing to negotiate a cipher (this causes the error "couldn't agree a client-to-server cipher") For some reason it is failing to resolve the name or complete a DNS handshake.
the same technology WinSCP uses
erm no. Both are layered protocols (usually running on top of TCP) but the lower layers are the same. Normally they both use the same port number.
(Windows) boxes
Presumably your employer hates its IT staff as much as mine.
From the networks point of view there is no difference between PuTTy and WinSCP. From the OS point of view, they are different programs. If they are behaving defferently then its because the OS is treating them differently. However if Applocker or your Anti-malware were responsible, then every winscp connection would be affected - not just that to this one target.
Have you checked there aren't problems with the name resolution? Before checking the hosts file and dredging through the registry for the search order, just try pinging the name and see if it resolves the correct address.
Have you checked that the same credentials work on a different machine? If different credentials work on this machine?
If so, then the next step would be to reinstall winscp. If that doesn't work, fire up wireshark and start diagnosing the network.