This is a list of known bugs or issues with the claiming process.
Error when signing: Method not found: '!!0 System.Array.Empty()'
This is caused when the version of .NET Framework installed on your machine is older than 4.6.1. Please update your .NET framework from Microsoft to the latest version, which can be found here: https://www.microsoft.com/net/download/Windows/run
Claiming tool "Invalid DER signature" message
This seems to be an issue with a very few private keys. It does not appear to be tied to any particular bitcoin client.
Status: Solution under investigation