Error while generating DDR2 IP core for CycloneIV in Quartus13.1

Hi all,

Can anybody help me out to remove the following error I am getting while generating the core.

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Error (332000): can't read "dqsclksource": no such variable

while executing

"create_generated_clock -multiply_by 1 -source $dqsclksource -master_clock $dqsclksource $dqspin -name $dqs_out_clockname -add"

(procedure "add_requirements_for_instance" line 263)

invoked from within

"add_requirements_for_instance $corename $inst t board ISI $DDR2_USB_phy_use_flexible_timing"

("foreach" body line 3)

invoked from within

"foreach inst $instance_list {

post_sdc_message info "Adding SDC requirements for $corename instance $inst"

add_requirements_for_instance $corename $..."

(file "DDR2_USB_phy_ddr_timing.sdc" line 635)

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If I comment those lines in .sdc file, I am getting similar errors for other variables.

Thanks in advance.