What error do you get?
Are you sure that you have recovered the files correctly? e.g. not accidentally use a Text Copy instead of a Binary Copy or somesuch? If the files have been recovered from "undelete" or a tape dump of the whole disk (rather than file-by-file tape), or somesuch then there is a high possibility that the file is not "intact" - that said, files usually attach even with a large amount of damage (that can then be review with DBCC CHECKDB)