Designer Error: "Index was out of range. Must be non-negative and less than the size of the collection." (4341284)

When attempting to edit a custom email template within Designer the following error is displayed:

"Index was out of range. Must be non-negative and less than the size of the collection."

WORKAROUND

Within Designer, change the Target format of the email template to Txt instead of HTML and commit the changes.

STATUS

This will be fixed in a future release of the product. If you require this immediately corrected, please contact Support for a hotfix referencing the defect ID 29148