When I run Export Hardware, I get a pop-up message stating:
However, the output files for the Block Design (BD) have already generated.
This will happen if the IP core in a BD is locked for any reason.
The Export_hw is calling generate_target all. It should only be looking at the state of Synthesis and implementation runs.
As long as the Block Design has been implemented, you should be able to export the hardware. To work around the issue, a user should update the IP cores and regenerate.
This issue has been fixed in Vivado 2015.3.