I found the answer in ExtremeXOS Feature License Requirements document.
"To run MPLS with BlackDiamond 8900 xl-series modules, a BlackDiamond 8800 series switch requires ExtremeXOS Release 12.5 or later, BlackDiamond 8900-MSM128, and BlackDiamond 8900 xl-series modules. No other modules are supported when MPLS runs on a BlackDiamond 8800 series switch with ExtremeXOS 12.5."