I did very nice time lapses with my 5dmk2, but now...

1)I noticed black frames among the good ones.

2) the preview in BULB mode become very slow.

I have to film tomorrow and I'm very insecure if that it's also affecting the movies and I don't want to have any bad surprise. Did happen to anyone?

I tried to find the latest firmware. but all links go to canon site and I cannot find where is the firmware update...

Any help? Thanks a lot!