At this point, I suspect that you still have at least one infected machine on your network. All it takes is one to re-infect the others.
You need to systematically isolate each machine, doing a complete scan using at least two antivirus scanners and then re-connect it to the network, but without sharing any folders or using password protected folders.
Only once you have completely cleaned every machine will you be able to re-activate sharing.
For more info on this topic, please visit these SearchSecurity.com resources:
This was first published in October 2003