When I try to run my test on my Ubuntu server with nunit-console, I get an error because he don't find the file.
System.IO.DirectoryNotFoundException: Could not find a part of the path "/var/www/test/SeleniumTest/SeleniumTest/bin\Debug/SeleniumTest.dll"
I think the reason is the backslash but this file is generated by visual studio.
The issue is caused by backslash. Ubuntu can't recognize the path. You can try to run dll directly instead of solution file. It should be fine.