Due to a problem in the Quartus® II software version 12.0, you may see this internal error if your design implements an ALTLVDS_TX megafunction with the
tx_outclock signal driving core logic. This internal error occurs for designs targeting Arria® V or Cyclone® V devices.
tx_outclock signal to drive core logic is unsupported.
The Quartus II software begining with version 12.1 reports an error message describing the problem instead of producing an internal error.