I am the other 550D user who reported a crash of the camera by using Helicon Remote (Win 7 64): Err 70 more and more frequent and then the camera totally blocked even battery disconnected.
Sent to Canon Maintenance (Vilma Sud Ouest, in France), where the electronic board has been replaced under warranty, but they forgot to connect the liveview/video, despite “control of all functions”

, and I had to send it again

; I am waiting for the final result.
According to my experience with two Canon 1000D and one Nikon D90 (in A or M mode, jpg or raw shooting), and to what I read in various forums about the failures of the 550D (and also 5D MkII), I feel that the origin of the problem is inside the camera, since it does not occur only with Helicon remote but also with others softwares, or just by using the video. There is probably an electronic weakness which is “stimulated” by the use of Helicon Focus. Canon cameras are cheaper than Nikon ones but not as much reliable; we get what we pay for…
Anyway, it will be helpful for all of us to have an overview of the frequency of this kind of trouble which occurs with high resolution Canon EOS cameras when using remote liveview, and to know which are the best solutions for avoiding them. Are such troubles systematic or limited to a bad line of production?