A few weeks ago I needed to queue up a script as a scheduled task. The script had a few string based parameters whose values contained spaces (e.g. MyScript.ps1 -ParamA 'My ParamA Value'). In order for my scheduled task action's add argument to work I had to use the following format. This also fixes the issue when you have spaces in your script name.
-WindowStyle Hidden "& \"C:\PowerShell Modules and Scripts\wsus_approveUpdates.ps1\" -group \"Print Servers - Prod\" -days 30"