Modelsim nativelink not working

I just upgraded to 10.1. The nativelink to Modelsim-Altera has stopped working. I looked at the xxxx_nativelink_simulation.rpt file and the messages don't give me much to go on:

"Error: Can't launch the ModelSim-Altera software -- the path to the location of the executables for the ModelSim-Altera software were not specified or the executables were not found at specified path."

I looked at the path settings and, after eliminating the path to the old v9.1 Modelsim directory, and verifying the path to the new 10.1 Modelsim directory, it still gives me the same error. The new Modelsim runs fine if I run it directly; that is, the license checks out fine. I can simulate a design. I just can't run the simulation from Quartus.

I looked through the EDA Tool Settings menu, and the Simulation "Tool Name" points to "Modelsim-Altera" as expected. I don't see any place where I can set the Modelsim execution path, though.

I tried looking through the modelsim.tcl file but couldn't make heads or tails of it.

I didn't see any environment variables that specifically pointed to a Modelsim directory.

Any thoughts would be appreciated.

[notes: Installation is to default directory. Am running windows 7/64bit. Also, I mistakenly downloaded, installed and then removed the "paid" Modelsim version instead of the "Starter" version before installing the "Starter" version, but there don't seem to be any traces of that left on my system]