Since comodo update to 8.1.0.4426 Unable to download .exe files with firefox

Comodo Internet Security - CIS Install / Setup / Configuration Help - CIS
1

Since this update I have been unable to download ,exe files with firefox 34.00.5. with the following message
C:\Users??\AppData\Local\Temp\DfmvLGYL.exe.part could not be saved, because the source file could not be read.

I have tried the following:-

  1. Have the same issue on my laptop and another desktop computer after the upgrade
    2 .Exiting comodo temporarily allows downloads normally.
  2. Google chrome downloads ok!
  3. I reinstated a previous image prior to the recent upgrade --no issues!
    5 I uninstalled comodo and clean installed COMODO Internet Security 8.1.0.4426 --This failed to load properly and gave a fatal error 1603.

All my computers are running windows 7

I would be grateful for some help/info on this problem