That's a strange error message - you can look for the file list yourself in /usr/lib/ipkg/info/
There will be a large number of files with the extenstino .list - these funnily enough list all the files installed for the package.
To find out where a program is (or which of multiple copies of a program) being run from, use
replacing "mplayer" with whatever program you want to find, it should return something like
bash-2.05$ which mplayer