Hopefully you got your error fixed. I too had the same error and searched many pages trying to find a solution. I eventually got it to work by accident. I have seen many people trying to get help on this across many tech forums. I am posting here in case this helps other people.
The error code 0x800ccc13 is generic. It can mean many different things on different version of outlook. To narrow things down you need to include whatever text that comes with the error, in this case: "Unable to connect to the network. Check your network connection or modem". Note that I have seen different messages included with this one error code so the text is important.
In my particular case, I could send and receive emails fine but I could not send emails with attachments.
Often, norton or some other anti-virus is suspected. However, I have seen numerous user report that the error persists even after they have disabled the anti-virus, re-installed it, removed it, etc. This may fix it sometimes, but many of the posts I have seen where people are talking about this error suggest it usually doesn't help.
Some people have reinstalled outlook, their TCP stack in windows, etc. Again, doesn't really help based on what people have said.
In some case, their ISP was blocking port 25. This is for outgoing connections. ISPs block this port to reduce spam across their network. Even when this port was blocked, it usually only affects people who were not using their ISP as their email provider. I use IMAP instead of POP and I use an external email provider (fastmail.fm). I found a handy way to test to make sure everything was clear between me an my provider: from your command prompt ("dos") telnet (your smtp addresss) (port you want to test). btw, if your are using windows 7 like me, telnet is not installed by default, select it in control panel/programs and features. When I tried to telnet my provider at port 25, the connection timed out. But when I tried port 21 (an alternate port provided by my email provider to get around ISP blocks) it gave me some weird system prompt. This means I was getting through. That answered a lot of questions for me and saved me messing with the firewall, port scanners, etc. I tried this with norton disabled and enabled and in both cases it got through.
However, something was still interfering with sending email through this port with attachments. I am using Outlook 2007 but I installed the latest version of thunderbird (2.0.0.21) and it had the same problem (different error message though).
So here's what worked for me. This probably won't work in every case. I turned on SSL and switched to another port. In researching solutions I noticed that fastmail accepts SSL for both sending and receiving. This is optional and I have never used it before. when I selected this in both thunderbird and Outlook 2007, it started sending attachments just fine, even with norton having all its checks turned on.
I suspect that there is something lurking in the TCP/IP stack of windows that is preventing any email program from sending attachments through the lower numbered ports. It now works either because I am using SSL (and this is considered more safe) or because SSL uses a higher port number for sending: port 465. SSL is an encryption protocol by the way.
So it works for now and I have been able to get back to work (I needed to send a demo to a customer). I hope this helps some other people.
