Critical Issue
Description
You may see this internal error when generating designs using ALTERA GPIO LITE megafunction. This problem affects the Quartus II software v14.0 and earlier when you upgrade to the quartus II software version 14.1. A true differential buffer does not support output enable (oe).
Resolution
To work around this problem, turn off any output enable (oe) related options when the design uses true differential buffer, then regenerate the design. This problem is fixed for new designs in the Quartus II software v14.1.