In general when signature errors occur it is usually caused by one of the following reasons:

1. The event handler, page generator and document template has not been re-generated and build in order to reflect the latest changes.
2. Fields that are part of the signature (In Hidden but not in ExcludeFromSign) are not present in WsyDetails or in WsyGrid in the page generator function. That is important because it is these values the signature will be based on. WsyGrid is used for Grid events whereas WsyDetails is used for events outside the grid.