I might be wrong and I dont have an Amiga anymore, but maybe you are missing an unpacker. Download http://aminet.net/util/pack/xfdmaster.lha and use xfdlist to see with what packer the files are packed with. After that search aminet for suitable unpacker if its indeed missing.
Just a tought and I might be totally wrong
ps. maybe xpk has similar command to tell the packer, see manual about the c/ commands