I tested, works (phonegap build service).
Did you try example_phonegaptoast.capx?
If not, try with example_phonegaptoast.capx.
Can you check the url text by Browser.Alert(PhonegapCapture.CapturedImage)
And check whether the url (file) exists. (specially after close app)
Probably you need pc itunes (?).
Try to check it and let me know the result.