Many scanners offer a possibility to scan to a network location. There are different possible protocols to transfer scanned files over the wire. Most popular are SMB and FTP. SMB uses UNC notation to scan to a network share on your PC (home version) or a server.
While it works fine for Windows XP you may encounter problems after switching to Vista. Same network, same share name, same IP address, same access privileges, but... the scanner reports "connection error" or "connection unavailable".
One of popular reasons is the difference in handling of SMB network packets between Windows XP and Vista.
What now? Check the MS KB article http://support.microsoft.com/kb/935755/, download the hotfix (available on the top of the page), install on your Vista, restart the box and scan the page again. Should work...