compile error with ddr2 sdram controller

[Altera_Forum]

hi everyone , 

I am using SOPC to control DDR2 SDRAM,when i set pin assignment to the SOPC system ,following error occurs: Error: Illegal connection found on I/O input buffer primitive image:inst|ddr2_sdram:the_ddr2_sdram|ddr2_sdram_controller_phy:ddr2_sdram_controller_phy_inst|ddr2_sdram_phy:ddr2_sdram_phy_inst|ddr2_sdram_phy_alt_mem_phy:ddr2_sdram_phy_alt_mem_phy_inst|ddr2_sdram_phy_alt_mem_phy_clk_reset:clk|gen_mimic_diff_ibuf.fb_clk_ibuf.  SourceIO image:inst|ddr2_sdram:the_ddr2_sdram|ddr2_sdram_controller_phy:ddr2_sdram_controller_phy_inst|ddr2_sdram_phy:ddr2_sdram_phy_inst|ddr2_sdram_phy_alt_mem_phy:ddr2_sdram_phy_alt_mem_phy_inst|ddr2_sdram_phy_alt_mem_phy_clk_reset:clk|DDR_CLK_OUT[0].mem_clk_obuf also drives out to other destination than the buffer.   when i have not set pin assignment ,and there is no error,is anyone konw the reason?thank you.

[Altera_Forum]

--- Quote Start ---  hi everyone ,  I am using SOPC to control DDR2 SDRAM,when i set pin assignment to the SOPC system ,following error occurs: Error: Illegal connection found on I/O input buffer primitive image:inst|ddr2_sdram:the_ddr2_sdram|ddr2_sdram_controller_phy:ddr2_sdram_controller_phy_inst|ddr2_sdram_phy:ddr2_sdram_phy_inst|ddr2_sdram_phy_alt_mem_phy:ddr2_sdram_phy_alt_mem_phy_inst|ddr2_sdram_phy_alt_mem_phy_clk_reset:clk|gen_mimic_diff_ibuf.fb_clk_ibuf.  SourceIO image:inst|ddr2_sdram:the_ddr2_sdram|ddr2_sdram_controller_phy:ddr2_sdram_controller_phy_inst|ddr2_sdram_phy:ddr2_sdram_phy_inst|ddr2_sdram_phy_alt_mem_phy:ddr2_sdram_phy_alt_mem_phy_inst|ddr2_sdram_phy_alt_mem_phy_clk_reset:clk|DDR_CLK_OUT[0].mem_clk_obuf also drives out to other destination than the buffer.   when i have not set pin assignment ,and there is no error,is anyone konw the reason?thank you.  --- Quote End ---   I met the same questions.When I add some singles into the SignalTap,it happens.