"Collection was modified; enumeration operation may not execute"

If you have created your own custom Windows Vista image (WIM file) and tried to use it with BDD 2007, Microsoft Deployment, or even with just the Windows System Image Manager tool, you may have run into the error above.  For the fix to that issue, see https://support.microsoft.com/kb/941595.  Be sure to follow the instructions carefully, as you will need to copy a new DLL into two places if you are using BDD 2007.  (That's not necessary for Microsoft Deployment as it uses the files directly from C:\Program Files\Windows AIK.)  And you'll need to create the new registry key before you'll be able to import any new updates or language packs.