Description
Due to a problem in the Quartus® II software version 13.0 Web Edition, you may see this internal error when launching the RTL Viewer.
Resolution
To work around this problem, edit your project Quartus II Settings File (.qsf) to include the following line (or modify this setting if the line is already in your .qsf):
set_global_assignment -name RTLV_GROUP_RELATED_NODES ON
This problem is scheduled to be fixed in a future release of the Quartus® II software.