Googling the above program reviews using WOT browser add-on yields many websites with poor to dangerous reputations. As in spam, malicious exploits, web malware. Here: http://www.mywot.com/en/scorecard/65.39.72.142
Please confirm the above program name is correct. WOT (Web Of Trust) here: http://www.mywot.com/ Program may itself by clean, but appears not to be compatible with Avast!, not the other way around. What if Avast is actually doing its job, and thus preventing you from becoming infected?
OK, I’ll say some more. There’s a sufficient number of legit sites that carry Great Owl. PNY is not supposed to distribute malware, so yes, you can trust Great Owl. I don’t know how good it really is.
Avast inhibits Great Owl either through its filesystem shield or (more likely in my opinion) behaviour shield. Vicky: can you mark Great Owl as a trusted process in behaviour shield? Open Avast user interface > Realtime Shields > Behaviour shield (that is with an U, avast, we are not in America!) > Expert settings > Trusted processes > Add > browse to Great Owl and select its executable.
If this does not help, you could try the same for Filesystem shield.