R CMD build - ERROR copying to build directory failed

I can't seem to build a new package that I created (not much other than the R generated skeleton). Here's the error message. How can I view more details about the ERROR? And where is the "build directory" specified?

Loading required package: digest
* checking for file 'E:\R\mypkg/DESCRIPTION' ... OK
* preparing 'mypkg':
* checking DESCRIPTION meta-information ... OK
 ERROR
copying to build directory f开发者_高级运维ailed

The issue is that I didn't have RTools installed http://www.murdoch-sutherland.com/Rtools/