Any attempt to generate a padded netlist for a multgen or ethernet_statistics core results in the following NGDBuild error:
ERROR:sim - NgdBuild:76 - File "./tmp/_cg/MultAdd.ngc" cannot be merged into block "MultAdd_top" (TYPE="MultAdd") because one or more pins on the block, including pin "p<0>", were not found in the file. Please make sure that all pins on the instantiated component match pins in the lower-level design block (irrespective of case). If there are bussed pins on this block, make sure that the upper-level and lower-level netlists use the same bus-naming convention.
The problem is that the core's padded netlist is being created with an incorrect index for any bus port that begins with a non-zero range.
For example, if a port P has range [43:2] (42 bits), the padded netlist is created with a range [41:0] (42 bits). The two ports do not match because of the difference in the range, which leads to the NGDBuild error.
This error occurs when IP core generation includes the generation of a padded netlist for any core that has a port with a non-zero lower range.
To avoid this error, de-select the Create Netlist Wrapper with I/O pads option under Project -> Project Options, Advanced tab.