Internal Error: Sub-system: SSYN, File: /quartus/synth/ssyn/ssyn_env.cpp, Line: 304

Due to a problem in the Quartus® II software version 12.0 and later, you may see the following internal error during synthesis:

Internal Error: Sub-system: SSYN, File: /quartus/synth/ssyn/ssyn_env.cpp, Line: 304
m_atom_node_vector[atom_node->get_id()] == 0

To work around this issue, turn off physical synthesis options by following the steps below:

1. Select Settings from Quartus II Assignments menu
2. Click on Compilation Process Settings in the Category window
3. Turn off the physical synthesis options under Physical Synthesis Optimizations

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