I’m making a guess here, but your start invocation probably looks like this:
start "\Foo\Bar\Path with spaces in it\program.exe"
This will open a new console window, using “\Foo\Bar\Path with spaces in it\program.exe” as its title.
If you use start with something that is (or needs to be) surrounded by quotes, you need to put empty quotes as the first argument:
start "" "\Foo\Bar\Path with spaces in it\program.exe"
This is because start interprets the first quoted argument it finds as the window title for a new console window.