Cannot find output terms for clock synthesis

Hi,

I am getting an error while doing clock tree synthesis in encounter 10.1. It showing that
**ERROR: (ENCCK-158): Cannot find output terms for clock clk_in/ANAIO.

Here pad inastant name is "clk_in" and pin name is "ANAIO".

Clock tree specification file is

        AutoCTSRootPin clk_in/ANAIO

        NoGating rising               # (for auto CTS on a net)
        Buffer HS65_LS_BFX2 HS65_LS_BFX4 HS65_LS_BFX7 HS65_LS_IVX2 // name of buffer used for CTS
       
       MaxDelay 5ns
       MinDelay 0ns
       MaxSkew 50ps
       End