Hi!
even if this is a very old thread I would like to post an answer for this problem because I was not able to find anything helpful in the web.
This is problem occurred when I tried to recreate and rebuilt my project when I didn't completely remove all files from the /sftware/project_sources directory.
Here what you simply need to do:
copy your sources in software directory for example
delete the two folders /sftware/project_sources and /sftware/project_bsp_sources
then recreate properly your bsp from eclipse (if you're under windows run it in administrator mode)
add your sources in /sftware/project_sources
built all
everything should be working fine.
hope this will help someone.