Sorry, I don't know the cause of your error.
Although I'm relatively new to FB (I've previously developed mostly in Flash Pro) I've run into something similar I think.
Sometimes FB is looking at object compiled and sitting in your debug-bin folder. After you fix a bug and it doesn't go away, then do a project clean and that might clear it up.
I have tried cleaning, and getting rid of the bin-debug, but the behavior seems to either come back quickly or not go away at all. I thought it was localized to new projects, but older imported projects are doing the same thing. Hopefully there is a permanent fix I am not seeing.
Looks like its dying on the first line of code in that method. Try checking:
The methods parameters - perhaps compiler doesn't like TextFormat defaulting to null
Or perhaps you're using that default null param and its biting you but misreporting the line number.
Seems like I might have had problems in the past with params, but I think it was with assigning null to a callback function param.
Instead I had it default to an empty class method called NullMethod, or some such.
Other ideas, although these usually apply to compile time errors and not runtime:
Import statements - are you missing one?
Access modifiers - is something trying to call this method that doesn't have access?
Check for syntax errors higher in the file.