Garden Ops is hosted by players. It's very hit and miss. A lot of times you can't join them because the host probably doesn't have his ports forwarded or maybe a firewall or something.
If it says "Connection Lost" that means the host left.
If it lags really bad (stutters, rubberbanding) and your getting a solid FPS (left CTL+R), the host is either really far away or has terrible internet.
Does it do the same if you play Multiplayer -> Welcome Mat or Garden vs Graveyards?
You could also try hosting your own Garden Ops.
The game itself isn't crashing is it?
**just read freezing up and it sunk in**... mmmm
Does it give an error message?
Do you have any overlay programs running like Fraps or RiviaTuner (comes with Afterburner) something along those lines?
Overlay programs and Origin In Game do not play nice together.