FitNesse regex get form title

I'm trying to get a part of the form title by using regex for a FitNesse test, but have been unsuccessful. 

If the form title is Review Work Order S191234, I want to grab only the S191234.

Here's the script line I'm currently using:

| $titly = |get regex       | S[0-9]{5,6}|group|1|get form title |

I've attached the error message.  Can someone please help?