Recently we encountered a warning message “Couldn’t lock the item LHSImage RHSCopy 2” when we changed an image of a custom email and click the save button. We have several custom Sitecore EXM email templates and most of them consist of few custom Sitecore components. “LHSImage RHSCopy 2” is one of the components in an email template. 
When one of our EXM users edits an image or text, he is actually editing one of the Sitecore components. Once the user clicks on save after the edit, that component/item gets locked for that user. Later, if any other user tries to edit the same component then he will see a warning message “Couldn’t lock the item…”.
Sitecore Admin can unlock the item.
Thanks
Munir
