grammar conversion

Hi,

I want to use  the following grammar which I have previously used in NLTK:

S -> L S |  L
L -> 'A' F 'U' | 'A' | 'U' F 'A' | 'U' | 'C' F 'G' | 'C' | 'G' F 'C' | 'G'
F -> 'A' F 'U' | 'U' F 'A' | 'C' F 'G' | 'G' F 'C' | L S
Nothing -> None


But it shows an error for the sequence "ACCCUGGAU" that "The given sequence is not in the language produced by the grammar". How can I solve it?