ModelSim error: Design unit not found

I originally placed this post on the Quartus II and EDA Tools Discussion forum a few days ago but have received no replies. I hope for better results here.

I'm trying to use ModelSim to simulate a Verilog design that requires the

megafunction lpm_mult. I have found entries for lpm_mult in the 220model.ver and

the lpm.ver libraries. In the Start Simulation window I have tried clicking on

(highlighting) one of these versions of lpm_mult in addition to my own project

files, but when I start simulation I always get the error message:

** Error: (vsim-3033) C:/Documents and Settings ... qmul_alpha1.v(57):

Instantiation of 'lpm_mult' failed. The design unit was not found.

qmul_alpha1.v is the file containing the reference to lpm_mult that was created

by the Megafunction Wizard.

What do I need to do to correct this?