Could be the write to card buffer problem, low battery, size of file you are using, using auto (it will try and alter settings for each shot), some of the things that could be a factor.
Hope this helps.
try manualylysetting the exposure, test different cards,
I've got a 450D and a 2Gb SanDisk card - I've not had any issues with continuos shooting so far ..... Has the issue only just started happening?

I only got the camera on thursday, and it was like it when it arrived.![]()
Oohhhhh I've sussed it! Phew!!
OK on the custom functions i had the high ISO speed noise reduction on.
In this mode you can only take 2 shots in a row.
Thanks all for the suggestions.
Hopefully this will help anyone that has the same problem![]()
So factory reset wroked , bet your well chuffed