Avast crashes trying to update virus databases

Avast Free Antivirus / Premium Security
1

this has started only recently. couple of days ago.
i haven’t touched AVAST in any way, but now every time it tries to update its virus databases (both automatically and manually), the app crashes (windows VISTA) with the following on-screen dialog presented by the OS:

Problem signature:
Problem Event Name: APPCRASH
Application Name: avast.setup
Application Version: 4.8.0.0
Application Timestamp: 482d2764
Fault Module Name: avast.setup
Fault Module Version: 4.8.0.0
Fault Module Timestamp: 482d2764
Exception Code: c0000005
Exception Offset: 0005021b
OS Version: 6.0.6001.2.1.0.256.1
Locale ID: 2057
Additional Information 1: 7136
Additional Information 2: 01ccbfe8524fff66028a6b5d6aa6614a
Additional Information 3: 1457
Additional Information 4: 0b09848753c439faaeb53538b700dd6a

2

Try to repair avast by going Add and Remove Programs>Avast>Repair

If the repair does not work, then Uninstall avast and reinstall.

3

Edit file setup.ini in avast4\setup folder and add the following lines:
[BufferLog]
Enable=1

Save the ini file, then start update. When it crashes, send me file SetupDbg.log from avast4\setup folder.
After that, remove those 2 lines from setup.ini.