The !-PathParser-! is used by the .NET !-FitServer-! to parse the path passed to it from [[!-FitNesse-!][.FitNesse]]. You can include a config file on the path, and .NET !-FitServer-! will use that config file during the test run.

Try just one path entry...
|path parser fixture|
|path string|assembly paths?|config file path?|
|c:\path\to\assembly.dll|c:\path\to\assembly.dll|null|

Now two...
|path parser fixture|
|path string|assembly paths?|config file path?|
|c:\path\to\assembly.dll;c:\path\to\other\assembly.dll|c:\path\to\assembly.dll,c:\path\to\other\assembly.dll|null|

Now one assembly and one config file
|path parser fixture|
|path string|assembly paths?|config file path?|
|c:\path\to\assembly.dll;c:\path\to\assembly.config|c:\path\to\assembly.dll|c:\path\to\assembly.config|