System.IO.File' does not contain a definition for `ReadAllBytes'

I buy Mobile Strategy Game Kit and I read the literature.
After importing Ngui and 2D Toolkit, I have this error message:

Assets/Scripts/Save/SaveLoadWWW.cs(127,51): error CS0117: `System.IO.File' does not contain a definition for `ReadAllBytes'

The error line is:

byte[] levelData = System.IO.File.ReadAllBytes(filePath + fileNameLocal + fileExt);//full local save file

You have an idea?
thank you,
Best regards.

Resolved, I change platform. The webplayer does not support ReadAllBytes.

Change platform.
Default platform is WebPlayer.