Error: [Common 17-36] Cannot write file [project_constraints.ucf]

http://forums.xilinx.com/t5/Hierarchical-Design/PlanAhead-cannot-write-to-ucf-during-runs/td-p/271092


I ran into this when I was copying over projects and just modifying the constraints. The solution is to: A workaround for this specific issue is to uncheck "Read- only" for the UCF file that resides in the folder <project_name>.runs/impl_1/.constrs

>> 11/25 Update

Okay this also sometimes happens to me even when the Read-Only IS unchecked, when that happens, I saw one poster that deleted the folder for the run (impl_1 typically) I just made a new run and it will go.