Ive found that the .bat files in the RailsInstaller\Ruby2.2.0\bin file includes a repo path to one "emachnic", This makes the path not able to be found on the users computer.
By changing the path on the last line to be the correct path to the ruby.exe I made it work for me. But this looks like a bug.
Fix:
Open C:\RailsInstaller\Ruby2.2.0\bin\rails.bat
Change the content to something similar to:
@ECHO OFF
IF NOT "%~f0" == "~f0" GOTO :WinNT
@"C:\Users\emachnic\GitRepos\railsinstaller-windows\stage\Ruby2.2.0\bin\ruby.exe" "C:/Users/emachnic/GitRepos/railsinstaller-windows/stage/Ruby2.2.0/bin/sass" %1 %2 %3 %4 %5 %6 %7 %8 %9
GOTO :EOF
:WinNT
@"C:\Users\emachnic\GitRepos\railsinstaller-windows\stage\Ruby2.2.0\bin\ruby.exe" "%~dpn0" %*
Save and it should work