get rid of your groups cache, then pull your dowloads folder out, and put it on the desktop. Then, start the game, begin a test house with no cc, with a single sim. Have that sim interact with a townie, and propose. My guess is, that will work, if it does, it's cc. The last time I had something similar to this happen, I had downloaded a house with a "custom mailbox" which I did not notice. The cc that interferes with personal interactions are the ones with interaction menus; mailboxes, telephones, etc. that are hacked. Do as Charley suggests: go here
http://www.simwardrobe.com/ and get the hack detector utility.