This problem affects all UniPHY-based external memory interfaces, including DDR2, DDR3, LPDDR2, QDR II, RLDRAM II and RLDRAM 3 products.
You cannot open and modify UniPHY-based external memory interfaces generated in Quartus II software versions older than 11.1. Designs including cores generated in pre-11.1 versions will not migrate to the newer versions of the Quartus II software.
The workaround for this issue is to recreate your external memory interface in a newer version of the Quartus II software.
This issue will not be fixed.