Yes. Mac files (especially applications) have resource forks in addition to data forks and both are needed for the file to be fully complete. Sometimes when a file is transferred on the Internet the resource fork is lost or the way the file is sent corrupts the file. A BinHex or MacBinary file avoids this problem but .sit files should be ok. Curiously though a .smi I looked at had a fairly sizeable resource fork so that might be why you're having a problem using the file.