550d tends to shut itself off when out of focus

[algi]

Hello there!

This is my first post ever. I tried to look up every information I need to post this question, but it was a bit overwhelming, so sorry if this isn't the correct form or place and please, tell me where to ask it and how if I screw up.

I have an EOS 550D with an EF 50mm f/1.8 II lens and I installed the nightly build. I used a Zoom H4n as a card reader. (First when I tried to install ML, I got the blinking, so I updated the official firmware, then I installed ML.)

Now, the first time I installed the nightly build, I made the error of just overwriting the new files. The result was that my camera shut itself off twice, both times when I turned the focus to the extreme.

Then I corrected my error: I deleted the autoexec file and the ML folder and copied the nightly files on the card.

This time it took more time for my camera to turn itself off, but it happened again when my focus was in the extreme.

Also, I noticed that video is written to the card slower. The bar that shows memory usage never appeard for me with this SD card (it's class 10), this was the first time I saw it. (It frequently appeares with my class 6 SD card.)

My question is: how can I avoid the camera shutting off itself.

I hope I didn't forget any important detail.

Thank you,
Gábor

PS. So, it happened again. I just switched my camera on and was playing around with it and after like a minute, it turned off itself. I have no idea why. Last time I could wander aroud in the menu for minutes.

PPS. Now my camera turns off even after I formatted the SD card.

[ItsMeLenny]

Is your battery fully charged?

[russellsnr]

Do you use a battery grip? if so is it tight?.
Have you tried another card without ML installed?