How can you repair a corrupt ntbackup (.bkf) file?

I've got a corrupt ntbackup file that won't open in ntbackup.

There are various utilities that a google search turns up that say they can repair the files. Do I need to use one or is there a simple way of using ntbackup to do this?

Update: This forum thread on tek-tips has some very useful information, like

Many thanks to Michael (aka mpears) for referring me to the free NTBkup software at http://www.fpns.net/willy/msbackup.htm. Using this software, I was able to recover thousands of files from a corrupted, 20-GB BKF file, saving hundreds of dollars and an untold number of hours in re-creating various documents.

As alternative you could try this commercial software for BKF recovery.

Kernel BKF File Repair - Recovers and repairs the files from damaged bkf archives corrupted due to backup interruption, virus attacks, crc errors or backup software corruption. It allows access to corrupt bkf files which can not be restored using the original backup software due to any kind of corruption.

There is also an open source project on SourceForge: JMTF

Good luck!