Hi, a couple of points:
1. the 'f' parameter to tar needs to be followed immediately by the tar file you are creating. when you do -cjfP somefile.tar data tar interprets this as 'create a tar file P and add to it somefile.tar and data. So change the order of your tar parameters so that f is the last one, or separate them into 2 blocks, e.g.:
tar -cjPf somefile.tar data
2. theres no need to create a list of files and pass those to tar since tar will add the contents of a directory recursively anyway.
tar -f somefile.tar -cjP data
should be sufficient.
tar -cjf somefile.tar directory