Description
If you implement the Low Latency PHY with channel bonding and fb_compensation mode in Quartus® II 12.1 for Stratix® V devices, and need to reconfigure the Tx PLL, you may get the fitter error above.
Resolution
You should add XCVR_TX_PLL_RECONFIG_GROUP assignments for the tx_pll of each channel to enable Tx PLL merging.
You can find the tx_pll name in post-synthesis results.