Hi ,
This issue mostly happens with the multiple edits on same public folder item with different sources.
So Please try to reduce to the number of access and test.
The following similar issue for your reference.
Conflict message:

http://social.technet.microsoft.com/Forums/en-US/exchangesvrclients/thread/687c2ce6-22a7-46d2-a17c-0d256f55c0b6

Other information for your reference.
Public folder conflict messages:

http://social.technet.microsoft.com/forums/en-US/exchangesvradmin/thread/9c4dfbab-20fa-4d91-ad3c-dabbf6b9a85f/




Wendy Liu
TechNet Community Support

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We are unable to open a public folder item. Instead, we are presented with a window that says Conflicting edits have been made to the same item. To resolve this conflict....
However, the area that is supposed to show the last edited info is blank, and we are unable to choose an item to keep.
Please help.

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Hi ,
The similar issue for your reference.
Conflict message:

http://social.technet.microsoft.com/Forums/en-US/exchangesvrclients/thread/687c2ce6-22a7-46d2-a17c-0d256f55c0b6

Public folder conflict messages:

http://social.technet.microsoft.com/forums/en-US/exchangesvradmin/thread/9c4dfbab-20fa-4d91-ad3c-dabbf6b9a85f/




Wendy Liu
TechNet Community Support

There is an amazing pack of free network admin tools. click here to download it