DateAxis Class... is currently not supported when exporting a chart to PDF, XPS or image file formats. This axis is exported as CategoryAxis.
We have an automated report generation process that currently uses COM to construct graphs in Excel, extract them, and paste them into reports. GemBox.Spreadsheet is an infinitely preferable tool for the first step (constructing the tables and graphs). Unfortunately, almost all of our graphs are time series; and the date axes, when exported as images, are unreadable.
This feature request has been implemented and is available in the latest versions of GemBox.Spreadsheet.