Please note that there are possibilities that you are using FAKE unoriginal Sandisk memory card
I'm using Sandisk Ultra 16GB with my 1D Mark IV and 60D,
never have any problems with burst shooting 10fps and movie
Where you bought it, is it a good reputation known store ?
I got the SD card from a shop in Funan where I often buy things for office use and the shop has been around for years with good services...so I do not think they will carry pirated stuffs.
Both the SanDisk Class 4 cards came in sealed packaging and both them are having the same problem in recording. Do not know what is wrong....and many people are facing the same issues with their 60D.