Strange error with QDR-II+ IP

We're using the QDR-II+ controller IP on the Stratix V 5SGSED8N. We'd like to have a single controller that can access 4x 144 Mbit QDRs (i.e. 576 Mb of accessible memory). Due to pin count issues, we'd like to do this with 4, 18-bit wide devices, like the Cypress CY7C2663KV18. So our 4-device wide interface will have 72-bit wide data interfaces.

Using the megawizard in quartus 12.1 64 bit, I've generated IP that appears to do this and a basic implementation. In the megawizard, I selected a device width of 36 using x36 emulated mode, and chose a device width of two. This does generate a 72-bit wide data interface. However, it won't place and route. It gives the cryptic error message:

Error (332000): ERROR: Argument <pin_object> is an empty collection. Specify one that is a non-empty collection.
    while executing
"get_pin_info -name $pin_info"
    ("foreach" body line 139)
    invoked from within
"foreach { inst } $instances {
    if {  } {
       #  Clean-up stale content
        unset pins
    }
    array set pins $qdr72_p0_ddr_db($inst)
    set ..."
    (file "qdr72/qdr72_p0.sdc" line 171)

which I assume are related to a pair of these Critical Warning messages:

Critical Warning: qdr72_p0.sdc: Failed to find CPS output for pin 

an archived version of the project is attached.

Has anybody seen this error before? What does it mean? How can I get around it? Is what we're trying to do actually supported by the IP (4x18)?

Thanks in advance :)