I have a one week old 30D.
I am using a 4gb Lexar 133x Pro CF Card.
I have taken several test shots without issue. I can fire off 10 shots in a row without locking up. Then 10 more, and so on. No problem.
When I choose Erase ALL on the camera it states busy, the card activity light stays on and the only way to stop it is too remove the battery.
Has anyone else had this problem?
I am using the latest firmware.

