I generate the output products for my design by selecting the Block Design in the hierarchy view and choosing "Generate Output Products" and then "OOC Per IP"
At this point I get the following:
export_simulation -of_objects [get_files C:/test/test.srcs/sources_1/bd/design_1/design_1.bd] -directory C:/test/_X_.ip_user_files/sim_scripts -force
This error occurs for designs with specific IP when running Vivado in a read only directory.
To avoid the problem, CD to a directory with read/write permission and open Vivado from that location.
The issue will be fixed in Vivado 2016.1.