Just updated over the top of 6.0.1091 and appears to be fine.
Seems there has been some compression to the setup_av_free.exe at 54.2MB much smaller than the 6.0.1091 installation file.
See
http://forum.avast.com/index.php?topic=76488.msg634347#msg634347.
There's not much difference between 6.0.1091 and 6.0.1119 Free installers if you downloaded after April 18th. Around 700KB.
File: D:\Downloads\John\setup_av_free.exe
Size: 56816368 bytes
File Version: 6.0.1119.0
Modified: Friday, May 06, 2011, 2:49:37 PM
MD5: 0AD991930AAFA761CFEC6B55B101FC54
SHA1: B6E8BE189223E4D46FCDD2A01CD6E93F2DCAD7C7
CRC32: 1F8518BD
File: D:\Downloads\John\Security CD\AntiVirus\setup_av_free601091.exe
Size: 56189640 bytes
File Version: 6.0.1091.0
Modified: Wednesday, April 20, 2011, 9:18:54 AM
MD5: B355C07A9EF81C73B75A537B20301888
SHA1: 8E6BE284623496109B3E2ABFDD10280069252E3C
CRC32: 868714FB
I added the 601091 to the filename when I saved it, before.