-- While trying to export a VFD (e.g: vfdbase export -f test ) the following message is received:
"VFD index integrity check : index file is CORRUPTED"

* When coming to VFD it is very important to have up to date export of the VFD. VFD exports are simple text file that can be viewed on any text editor which contains the VFD tree but never the transfers or files information.

To generate a backup of the VFD you'll have to run the following command:
vfdbase export -f filename
The filename being the name of the file you will export the VFD to. Also a filename.log file will be created containing the log of the export which should contain the following.
Verification complete
VFD index file is correct.

There very little things that can be done when VFD get corrupted. Usually VFDs do not get corrupted unless deprecated versions of the navigator are used to create / update VFDs.  
It is critical not to keep running Gateway with corrupted VFDs, the corruption can only get worse up to a point it will bring Gateway down.

Here are the steps to follow if you have corrupted VFDs that you don't have an export:
" Stop Gateway,
" Run pelmon check_base -ra
" Start Gateway to check if it resolved the issue.

If it did not resolve the issue:
" Stop Gateway.
" Make a physical backup of your runtime/vfd directory.
" Run vfdbase export -f filename
" Delete the content of your runtime/vfd directory.
" Run vfdbase import -if filename
" Run pelmon check_base -ra
" Start Gateway to check if it resolved the issue.

If it did not resolve the issue:
" Stop Gateway.
" Delete the content of your runtime/vfd directory.
" Run pelmon rebuild_vfd
" Start Gateway to check if it resolved the issue.

If it did not resolve the issue your VFDs are not retrievable from their current status.
You'll need to import them from an older VFD export:
" Stop Gateway.
" Delete the content of your runtime/vfd directory.
" Run vfdbase import -if filename
" Run pelmon check_base -ra
" Start Gateway to check if it resolved the issue.

If you don't have an older export you still can import the VFD from a backup (as long as it is from the same patch level):
" Stop Gateway.
" Delete the content of your runtime/vfd directory
" Copy the runtime/VFD content of your backup to your current runtime/vfd directory
" Run pelmon check_base -ra
" Start Gateway to check if it resolved the issue.

If it did not resolve the issue:
You'll have to create your VFDs from scratch on a backup Gateway (same platform and patch level) with no transfers then export them to the corrupted Gateway.
Backup Gateway:
" Start Gateway
" Create your VFDs manually using the GUI.
" Export your VFD

Corrupted Gateway:
" Stop Gateway.
" Delete the content of your runtime/vfd directory.
" Run vfdbase import -if filename
" Run pelmon check_base -ra
" Start Gateway.