note also that the "mimetype" file must be exactly 20 bytes in size (compressed and uncompressed). if it isn't, something is wrong.
Example:
Code:
$ unzip -v elBrujo.epub
Archive: elBrujo.epub
Length Method Size Cmpr Date Time CRC-32 Name
-------- ------ ------- ---- ---------- ----- -------- ----
20 Stored 20 0% 2011-11-11 17:12 2cab616f mimetype
259 Defl:S 180 31% 2011-11-11 17:12 9aa7f027 META-INF/container.xml
7122 Defl:S 1612 77% 2011-11-11 17:12 2079d1c6 OEBPS/content.opf
5742 Defl:S 1070 81% 2011-11-11 17:12 f6ff143a OEBPS/toc.ncx
...
etc.