Problem: The following error might appear when you try to add a custom Windows Vista Windows Imaging Format (WIM) file to the Deployment Workbench:
Error during wizard processing
An unexpected error occurred while processing the wizard results.
Collection was modified; enumeration operation may not execute.
Possible Solution: You can resolve this issue by applying the update mentioned in the Microsoft Support article You cannot create a Windows Vista-based WIM build in Solution Accelerator for Business Desktop Deployment.