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In the Wallet go to “Tools” → “Wallet Repair”
Select “Delete local Blockchain Folders”
This process will delete any non-crucial files and folders to be able to restore/resync re-sync once more from scratch.
If for some reason you still encounter issues of any form when synchronizing your Wallet. Then please follow these steps below:
Close the Wallet
Open the %appdata%/rpicoin folder (linux: ~/.rpicoin/ )
Delete all the files as shown in the screenshot
Start the Wallet and let is fully sync