Before having a laptop with Vista, I'd previously run two separate windows from a single .exe file by specifying the "-r" command line switch using separate directories.

The shortcuts looked like this:
Name: production_client
Target: "C:\Program Files\mIRC\mIRC.exe -rC:\Data Files\mIRC\ProductionClient"
--and---
Name: test_client
Target: "C:\Program Files\mIRC\mIRC.exe -rC:\Data Files\mIRC\TestClient

Under Vista, the Target form given above produces an "Invalid File Name" error message when trying to save the shortcut.

By altering the Target slightly I can save the shortcut, but it does not cause mIRC to start using the desired directory. Here is an example of the alteration:
Target: "C:\Program Files\mIRC\mIRC.exe" "-rC:\Data Files\mIRC\TestClient"

Instead, mIRC starts using .ini files found in C:\Users\<user-name>\AppData\Roaming\mIRC which were placed in that directory during the installation process.

<user-name> is the owner of the C:\Data Files\mIRC directory and the directory's permissions have been set to read-write for the directory itself and all files.

This seems to me to be a Vista command interpreter problem, but am hoping someone has a workaround or suggestions for how to construct the Target of a shortcut to permit running separate scripts in two different windows.

Just a guess, but perhaps:
"C:\Program Files\mIRC\mIRC.exe" -r"C:\Data Files\mIRC\TestClient"
?

to 5618:

Thanks! that actually seems to have done the trick nicely! While it still is a change in behavior from Windows NT/2000/XP that I would categorize as a Windows bug, you nailed it. I'd stopped my experimentation before exhausting all the possibilibities.