You didn't look hard enough for an answer. A quick check of the help files searching for Disk Cache turns up this:
The Maximum Disk Cache Size setting specifies the number of gigabytes of hard disk space to use. In After Effects CS6, the default disk cache size is set to 10% of the volume's total size, up to 100 GB. In After Effects CS5.5, this amount is 20 GB, by default. Because of this, many more frames are eligible for disk caching than in previous versions.
In After Effects CS5.5, the application checks to make sure that you have 10 GB free above what is set in Preferences > Media & Disk Cache. After Effects warns you if there is not enough room for the disk cache
100 GB should be plenty for AE even if you ware working on many projects at the same time. Also, make sure you understand what the disk cache does. You may be making incorrect assumptions.
Thanks for the reply Rick-
While it is true that I don't necessarily need over 100GB in cache, that in itself is not the issue. I want this error to not popup every time I open AE, or to be safe in the knowledge that this error can be safely ignored in my particular instance.
The default cache values don't really affect my situation as I am using a dedicated drive for caching.
I also have much more than 10GB free above what is set in my preferences. In all cases I have at least 40GB free above the specified amount.
What I would really like to know is if it is an inherent fact that when using a dedicated cache drive you can't set the AE cache value above 50% of the drive's capacity without getting this error when the drive begins to fill up?