You need to place exclusions for the two programs between each other, add the comodo program file to the exclusions in the avast file system shield and all avast processes need to be set to allow all in the comodo apps list.
There should just be three exe services to set to allow all which are avast gui, avast sevices and avast setup, you might hve to run a manual avast update before you see the setup exe.
I have a couple of systems with CIS ver5.8 Stable --one XP SP3 and a Win7 x32 with Avast IS(no firewall). In the Win7 system there is no exclusions placed on both Avast/CIS(from versions 5.5/5.8Beta and now ver5.8 Stable).
But in XPSP3 system with CIS (ver5.8Beta then) I had to place exclusions in CIS because it showed a pop-up about avast.setup(that was a surprise) and it seemed that it had a hard time learning the rules although it is in Trusted. Same with CIS version5.5 Stable. Now with CISver5.8 Stable there is no exclusions now.
Previously exclusions (when using CISver5.3 till ver5.4) I place the: