PS+ has nothing to do with connection to games, its just extra stuff in the PSN store (free games, discounts etc).
But yeah, Black Ops, worst game for disconnections ever. I've given up with it, BFBC2 has new maps & its playable.
My issue is usually before I even get into the game. I fire up the PS3 and it signs me in to PSN just fine...then I start Black Ops, and more times than not, it tells me an error has occured and i've been signed out of PSN while it's still loading the game, before I get to the "press start" screen. When I start the game and try and get online to play zombies, it won't sign me back into PSN. I check the network connection and everything is fine (IP, interent, PSN), but it still won't sign me in. I can restart my PS3, router, modem...and go through the whole thing all over again. Everything I restart my PS3, it signs me into PSN just fine, but when I start Black Ops? It's hit or miss. And yeah, of course I get kicked from games some times too. Extremely frustrating.