Stratix IV problem with pin assignments

Hello,

using the SOPC builder in combination with the Stratix IV EP4SGX230KF40C2 on the Stratix IV GX development board I encountered several problems with the pin assignments. My aim is to integrate one of the DDR3 memories into my system.

Assigning the signal provided by the SOPC, being called mem_clk_n_to_and_from_the_altmemddr_0 to I/O standart SSTL-15 Class 1 on Location PIN_AF20 as described in the boards documentation on page 2-50 I get the following error, performing an I/O check or a full compilation:

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Error: Can't place node "mem_clk_n_to_and_from_the_altmemddr_0" -- node is a differential I/O node

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Just in case I change this signal to a differential standard and assign it to some free differential pins, re-compiling will result in complaining about the same error on other pins.

Thanks in advance.

Sebastian Feger