Personally I would want to know why that program feels it necessary to disable your AV, this is such a prehistoric concept. I would want to know what it does that might be considered malicious by an AV, effectively I would want to know what it has to hide.
I don't disable avast to install programs as this is the very time that I would say your defences should be up and not have your virtual security trousers round your ankles.
I take it that you are using avast 4,8 ?
If so, Left click the avast icon, (if there is a Details...>> button click that) now select the Standard Shield provider and click Start.