Duplication appears in system folders and/or in shared folders
If two or more computers share a common PST file then they should not be configured to also share data using WorkgroupShare.
This is because as soon as an entry is created in an Outlook folder on one client it will immediately be reflected in the other clients through the PST file. Then, WorkgroupShare will share this entry and a copy will be created in any client with read access to this folder. If this happens on a client that shares the same PST file then duplication of each new entry will result.
To prevent this from happening, configure each copy of Outlook to use an independent PST file before installing the WorkgroupShare client software.
If duplication of data has already occurred, the first step in correcting the problem is to ensure that each instance of Outlook has a unique PST file. This will leave one copy of Outlook with the original PST file with the duplicated data. This duplication can be removed from the WorkgroupShare database by using the duplicate removal tool. Refer to FAQ How do I remove duplicate items from a shared folder. Once the duplicates have been removed, the changes will be synchronized to the client when it next connects to the server.