I've had this problem on more than one printer, so I believe the issue is to do with the computer that I intend to scan documents to.
On two different multifunction printers (HP and Canon), I've attempted to set up scanning to a share on a Windows 7 machine.
In the printer's web UI, it gives me options to put the computer's hostname (or IP), the share folder, and a username/password.
It doesn't matter whether I use hostname or IP, the scanner cannot connect to the remote computer.
I can ping the printer from the computer. Permissions are set up for the username that I've set up.
I'm wondering if there is some sort of firewall or antivirus issue blocking the connection, but I don't even know where to start. There isn't dedicated software I'm using to scan, it's just a direct Windows SMB scan.
As far as error messages go, on one printer I got a generic "Can't Connect" error. On the one I'm currently trying to set up (Canon), I get an "Error 806", which is a credential error, but I am absolutely positive I have entered the credentials correctly.
Best Answer
I've made a few comments above, but in the meantime check your Windows Firewall. Is Port 445 open?
EDIT:
Digging deeper into Canon's site, I've found the following:
Blocked Ports and Programs
In some cases, third-party security or firewall software may be blocking or restricting port traffic or programs causing unexpected results such as inability to install or loss of functionality. Check with the software manufacturer for information on unblocking ports or adding exceptions for specific programs.
The following are ports and programs necessary for your printer to function properly.
Ports
TCP 80
TCP / UDP 8611
TCP / UDP 8612
TCP / UDP 8613
UDP 3702 - (Windows 7 / Windows Vista)
The following port list applies only to models with memory card slots TCP / UDP 137
TCP / UDP 138
TCP / UDP 139
Programs
IJ Network Tool
Default location
c:\Program Files (x86)\Canon\Canon IJ Network Tool\CNMNPUT.EXE (Windows)
/library/printers/canon/bjprinter/utilities/canon ij network tool.app (Macintosh OS X)
IJ Network Scan Utility
Default location
c:\Program Files (x86)\Canon\Canon IJ Network Scan Utilityl\CNMNSUT.EXE (Windows)
/library/printers/canon/bjprinter/utilities/canon ij network scan utility.app (Macintosh OS X)
IJ Network Scanner Selector
Default location
/library/printers/canon/ijscanner/utilities/canon ij network scanner selector2.app (Macintosh OS X)
MP Navigator EX
Default location
C:\Program Files\Canon\MP Navigator EX**\ mpnex**.exe (** refers to version number) - (Windows)
/application/canon utilities/mp navigator.app (Macintosh OS X)