.gitignore vs untracked working file

Hi

I have a .gitignore rule to ignore everything in bin/ directories but
I cannot change branch because of a file lying in a bin/ directory
which actually should be ignored. What am I doing wrong?

$ git branch
  master
* mybranch

$ git status
# On branch mybranch
nothing to commit (working directory clean)

$ cat .gitignore
*.class
.cvsignore
CVS/
.metadata/
build/
bin/
.#*

$ git checkout master
error: Untracked working tree file 'Project/bin/path/file.jjt' would
be overwritten by merge.

$ git --version
git version 1.6.4.msysgit.0


thx

Bost