If you try to import a file and you get the following error:
IMP-00010: not a valid export file, header failed verification
IMP-00000: Import terminated unsuccessfully
The cause according to Oracle error description is “Either the file was not generated by Export or it was corrupted”. The first obvious reason might be that the file is corrupted. However, if you downloaded it correctly (using binary transfer in the FTP as opposed to ASCII transfer) and you have no other reason to believe that the file is indeed corrupted. You might want to explore other options.
The most common reason for this error is mismatch of IMP and EXP versions. While it should not be a problem to import a file that was created with an earlier version of EXP using a newer version of IMP, trying to use it the other way will generate the above error. In other words, you can import a file that was created with 10g version of EXP using a 9i version of IMP. If this is the case, try to export the file using a lower version of EXP or try to import the file to a higher version Database. Later you can export it again using a lower version of the EXP utility.
Another reason, over looked many times, is that the file was exported using Data Pump (EXPDP not EXP) . If you are not the one who exported the file, try to restore it using the Data Pump import utility IMPDP. Since Data Pump is gaining traction and it is creating .dmp files it is possible that the dmp file in your hands was created using it.