[R] "couldn't find function" error message in R 2.1.1

[qikai xu]

Dear R-help,

I have a home-made package works perfectly under R 1.9.1.  Now I'm trying to
port it to R > 2.0.  So I rebuild the package under R 2.1.1. It installs and
loads OK. But when I try to call some functions "myfoo" in this package, it
returns error message: "Couldn't find function myfoo".  I checked all
available manuals, and didn't find any specific requirement that I'm
violating.  Have anybody in the list ever had similar problem before and how
did you solve it?  Thanks a lot for your help.

Qikai Xu