I am using the 30664 I believe this is the most recent beta release of Avast!
What actually happens is when you click on the page Firefox want to save the login.php file as an empty text file. On Chrome I get an error message, and Safari is just blank. I'm not at the computer right now so I cannot give specific error messages. The site is a private work site so I cannot give that either.
I have downloaded the file but I did not see any indication of a virus, as the text file is empty. I can get around this just by turning off the webshield. This may be an isolated bad coding of a website, I just think it's odd as the website has not changed, and I just recently started seeing this error. I even tried it on a Windows 7 box running Avast! and there was no issues. Both my Macs running Avast! exhibit the same behavior.