How to split a string using unity flash player?

I am currently working on a game to be distributed on Flash, in my code I need to split a string(in this case, getting some html parameters).

 Application.absoluteURL.Split ("?"[0])[1].Split ("="[0])[1];

This is fine in the editor, however when I try to build the player I get many complier errors. One like this:

 Error building Player: Exception: java Failed:
 Loading configuration file C:\Program Files (x86)\Unity\Editor\Data\PlaybackEngines\flashsupport\BuildTools\flex\frameworks\flex-config.xml
 
 C:\Users\Nick\Documents\UnityFacebook\Temp\StagingArea\Data\ConvertedDotNetCode\global\FacebookManager__Start_c__Iterator1.as(47): col: 207 Error: Call to a possibly undefined method String_get_Chars_Int32 through a reference with static type Class.

And 4 similar to this:

 C:\Users\Nick\Documents\UnityFacebook\Temp\StagingArea\Data\ConvertedDotNetCode\global\FacebookManager__Start_c__Iterator1.as(47): col: 207 Error: Call to a possibly undefined method String_get_Chars_Int32 through a reference with static type Class.

I am sure it is this line of code that is causing the error as when I comment it out the game builds fine.

Does anyone know of a better method to split strings? Or what I am doing wrong here?

thanks in advance,

Nick

Additional Information:

• I am storing the split string value in a serialized class I have written myself

• I am using unity 4

• I have tried reloading unity and running as an administrator

• Running Windows 7

• Building to Flash 11.4 (have tried others with same errors)

• Writing in C#