when i tried to import the hdl file to simulink, i got the following error message

Hmmm, you shouldn't have to copy those files into that directory. They should be picked up automatically. Certainly I've never needed to do that. On the other hand, if it works...

Have you tried upgrading to DSPB and Quartus 9.0?

One possibility is you have an interaction between different versions of DSPB and Quartus. Do you have more than one version installed? If so make sure that QUARTUS_VERSION and any paths in PATH point to the right versions. Also please delete the DSPBuilder_<mode>_import directory and try regenerating.

If all else fails you could try posting a cut down model that fails along with verilog source code and I can try to replicate.