Email attachments blocked

[Telegraph_Sam]

I use Yahoo Mail within Chrome on a Windows XP platform protected by Avast Free 2014.9.0.2007 and Comodo Personal firewall.  I don't download attachments to emails very frequently but in the past there was not a problem.  But just now I find that downloading even a pdf from a trusted source (I have tried more than one) no longer works. There is a link at the bottom of the email which you click on and up pops a screen asking you if you want to save it to the PC (you can't view it directly).  If I click on this link in the usual way there is a 2 nanosecond "scanning attachment" (I think) screen and then nothing.  Ditto with repeats.  I have searched on my hard drive to see if the file has somehow got saved - nothing.   Something I assume must have changed in the settings to make Avast (or possibly I suppose some other filter) super sensitive to all attachments.  How can I check and amend this?
I have been having go-slow problems with the PC recently and an Avast boot time scan and Ad-Aware identified some infected files (which Malwarebytes missed) which they have quarantined.  The latter two programs should not be running concurrently with Avast, only when I demand a scan.
What can I do?  Tks

[olddog]

You could try

(a) Disable Avast browser add on/ext
(b) Update to current 2014.9.0.2008 version

[Telegraph_Sam]

I intend to try your suggestions in sequence, tks.
Re 1 - are you referring to what is listed in my Chrome extensions as
"Avast! online security 9.0.2005.45" with the box opposite ticked as "enabled"?
If I disable this will I not deprive myself of all Avast online protection (throw the baby out with the bathwater?!)

[Telegraph_Sam]

"You could try

(a) Disable Avast browser add on/ext
(b) Update to current 2014.9.0.2008 version"

I have now done b) followed by a).  Downloading of pdf's etc attachments seems to be blocked after scanning as before.  Hardened Mode is only Moderate.  This is getting to be problematic.

[olddog]

Re 1 - are you referring to what is listed in my Chrome extensions as
"Avast! online security 9.0.2005.45" with the box opposite ticked as "enabled"?

Yes, disable that

If I disable this will I not deprive myself of all Avast online protection (throw the baby out with the bathwater?!)

You will still be protected by the web shield. You will lose web rep and some anti tracking functions, but the anti track seems to be causing more problems than it is worth.

[olddog]

..Downloading of pdf's etc attachments seems to be blocked after scanning as before.

Try turning off intelligent stream scanning. Avast GUI->Settings->Active Protection. Click on the little cog in Webshield, untick the box for "Use intelligent stream scanning" then click on OK.  After exiting Avast GUI it may pay to reboot.

From the help file:-
" When checked, files that are downloaded are scanned in real-time i.e. during the actual download process. The packets of data are scanned as soon as they arrive - and the next ones are downloaded only when the previous packets have been verified to be infection-free. If this feature is disabled, by unchecking the box, the whole file will be downloaded to a temporary folder first and then scanned.

Hardened Mode is only Moderate

I don't personally have hardened mode enabled at all.
In the moderate setting no files with poor reputation will be allowed to run. I'm not sure why this should affect a pdf attachment, but try turning off hardened mode anyhow and see whether it makes any difference.

[Telegraph_Sam]

"Try turning off intelligent stream scanning. Avast GUI->Settings->Active Protection. Click on the little cog in Webshield, untick the box for "Use intelligent stream scanning" then click on OK.  After exiting Avast GUI it may pay to reboot."

I have now done this including the reboot and checked that the Chrom Avast Online Security extension is disabled.  But I can still not download (pdf / jpg) attachments - which appear not to get past the automatic scanning process.  Yet I was able to download one of these Yahoo Mail attachments on another PC which was also running XP but not Avast, all of which points the finger of suspicion at version 2014.9.0.2008.  >> Disable Avast altogether???  Rather negates the point of having security in the first place. Has no one else with this version had the same problem, or got any other ideas?

[Alikhan]

http://forum.avast.com/index.php?topic=143211.0

[Telegraph_Sam]

Thanks, you will see that I am pursuing the topic on the forum link that you have kindly provided.