Im getting this error message telling me that the image buffers of size 28553 x 27787 @ 8bpc (3.0 GB

I'm new to AE, but have been able to modify projects and this is the first time, I've gotten this type of error, so I don't know how to resolve it.

I'm using an iMac, 27", 3.4 GHZ Intel Core i7, 16 GB memory, 1333 MHz DDR3, running, OS X 10.8.3. Thanks in advance.

Jose.