[R] write R extenesion issue

[jiesheng zhang]

Hi, all
I am trying to write a R package. I was able to build and install the 
package with no problem.
However, I got this error when I try to load the library by calling 
library("btRRTest");
------------------error message in loading---------
 > library("btRRTest")
Error in library("btRRTest") : 'btRRTest' is not a valid package -- 
installed < 2.0.0?
---------------------------------
--------build message-----------
ason at jasonportal:~/tmp2> R CMD build --force btRRTest
* checking for file 'btRRTest/DESCRIPTION' ... OK
* preparing 'btRRTest':
* checking DESCRIPTION meta-information ... OK
* cleaning src
* checking whether 'INDEX' is up-to-date ... NO
* overwriting 'INDEX' as '--force' was given
* removing junk files
* checking for LF line-endings in source files
* checking for empty directories
* building 'btRRTest_0.0.1.tar.gz'
---------------------------------
-------install message-------
jasonportal:/home/jason/tmp2 # R CMD INSTALL btRRTest_0.0.1.tar.gz
* Installing *binary* package 'btRRTest' ...
* DONE (btRRTest)
----------------------


Can anyone tell me what are the possible causes for this error? Where 
should I start to look?

Thanks

-jason