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You can usually ignore this message. To replace an existing source with a new one, delete the existing source first before importing. You can also edit the source to fix any errors.
"
The 
The following elements were skipped because they do not map to any biblio fields: Y2, AN, L2, L1"
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If you don't need the fields, you can ignore the error message. If you do need the fields, message mandala@virginia.edu with the Zotero field you need to add, and what you think the matching Mandala field should be.
"Can Can't flip around multiple ',' characters in "First Name,,Last Name"
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- Edit the source in Mandala
- In the Authors section, remove the extra comma
"Couldn Couldn't find a last name in 'author name'"
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