Hi, I have done some searching on the net, and it seems that you are not the only one with problems with Canon LBP5050 and more difficult firewall setup and/or network topology. To me it seems the drivers have or might have some problem obtaining the IP address of the printer, maybe there is some supporting service or app that is used to query just that which hasn't got the sufficient firewall rights.
If that would be the case, the app might broadcast some requests in such a way, that specifying the printer address in the Friends group (and/or creating a rule with the printers IP destination address and ALL Protocols/All directions = ALLOW) in the packet rules dialog is not enough.
Do you have the firewall set to ask/auto-decide so that new apps requesting the communication will be automatically added to your rule set?
Aren't there any app entries for the Canon related software that are blocked?
Is the IP address of the printer fixed? (not changing after reboots/restarts of the printer?) E.g. reserved in the DHCP of configured as fixed?
Do you have the IP correctly entered in the printer properties, or do you use some name resolution (another possible point of failure if anything gets blocked) ?
Wouldn't the following tip to setup/verify IP address of the printer be applicable to your printer as well?http://www.canon.co.uk/Support/Consumer_Products/products/printers/Laser/i-SENSYS_LBP6300dn.aspx?faqtcmuri=tcm:14-707049&page=1&type=faq
Here is a link to the discussion about a similar (maybe) problem. Would any of the suggestions there help?http://fransmayra.fi/2010/07/29/canon-lbp5050n-network-board-error/
I understand, you are seeing this as a problem with Avast firewall, since apparently all that is enough is turning it off - but not having the printer here for testing, I can only guess what are all the required configuration options needed for its correct communication.