I have tried to export gbXML file fro Revit and open it in Ecotect, DDS-CAD Viewer and I received errors saying that it cannot be opened. Here is the error that I have received in Ecotect:
"Warning: IFC support is only at beta stage in this release. Whilst detailed geometry should import, ifcSpace data and complex curves may not transform correctly."
Since Ecotect reads UTF-8 and Revit 2013 exports in UTF-16 format, Ecotect throws this exeption about icf.
How to solve this problem: Open your xml file with Notepad. In the file menu, Encoding change it to UTF-8 and then save your file. The following image shows this process.
Hope it works for you too.