Internal Error: Sub-system: VPR20KMAIN, File: /quartus/fitter/vpr20k/vpr_common/place_constraints.c, Line: 896

This error may be seen in the Quartus® II software version 9.1 when non-rectangular LogicLock™ regions are used in a design.

To work around this problem in the Quartus II software version 9.1, follow the steps below:

1. Create a text file named quartus.ini in your project directory, unless one already exists.
2. Add the following text to the quartus.ini  file: 
   disable_new_non_rectangular_region_support=on
3. Restart the Quartus II software to make use of this .ini variable.

This problem is scheduled to be fixed in a future release of the Quartus II software.