When you try opening tait30.exe what message do you get?
So you did not actually block a website, you blocked or maybe quarantined a program. Not certain if you blocked it with the firewall or quarantined it in the chest. Do you remember any of the information in the alert message? Deny sounds like firewall rule though and obviously you found that a default rule was created but cannot find it in the Application Rule list. Did you expand each group by clicking on it?
1. Are you certain you haven't overlooked it? Have you double-checked your firewall rules? Might be under a group named "Other" or "myitlab" or "Zeus Learning"? Have you looked in your virus chest? Virus chest is located under the maintenance tab. Maybe you quarantined it.
If you did then remove it from the chest. Before doing so, make 100% certain that it is not a malicious program.
2. If it is not in your virus chest then will you find the "rules.xml" file and read through it to see if it is in there?
Path for Windows 7 is:
C:\Users\All Users\Alwil Software\Avast5\fw
You will have to show hidden files and show operating system files. See attachment.
3. Some details on tait30.exe
http://www.prevx.com/filenames/X506941508057697078-X1/TAIT30.EXE.html