Here is a photo
http://i48.tinypic.com/2z9lefq.jpg
I'm not sure why the network shield would get involved here as generally it checks any connection requests against its malicious sites list and alerts if one is found, but you aren't getting any alerts. Whilst I have seen some avast alerts (in the forums) in relation to seeding URLs being considered malicious, I haven't seen any related to 'Tracker sending invalid data.' That was usually resolved by clearing the cache and any seeding URLs.
So I'm not sure what this invalid data might be (I don't use any P2P application), I don't know if the data you have obscured in the image might help someone else who does use P2P.
I ignored the network shield interaction temporarily to do a search on the error you were getting,
http://uk.search.yahoo.com/search?p=torrent+trackers+"Tracker+sending+invalid+data" and that gets lots of hits. Now if it is possible to get this for other reasons other than 'every one of this hits running avast (highly unlikely),' so there may be more to this as some firewalls also seem to have this impact.
Since the network shield is like a limited firewall if there happens to be any conflict between the firewall and the network shield removal one one element would resolve any conflict.
Unfortunately my practical experience with P2P apps is zero, so hopefully someone else can pick this up. However I would recommend that you create a new topic so that your problem doesn't get buried in this very large topic.