Depending on your requirements and environment, you need to match the PowerTools and OpenXML SDK versions.
PowerTools 2.2 (which right now is the default download on codeplex) uses DocumentFormat.OpenXml version 2.0.5022.0 which comes with OpenXml SDK 2.0.
This project is built on .NET Framework 3.5.
PowerTools for OpenXML 3.0 version 3.* (also available to download at https://powertools.codeplex.com/releases/view/74771) uses DocumentFormat.OpenXml version 2.5.5631.0 which comes with OpenXml SDK 2.5.
This project is built on .NET Framework 4.0+.