Text vectorisation operator

My Text Vectorisation operator is asking me to specify at attribute, but the drop down menu is blank. It seems the data might not be pulling through, but I cannot understand why not or what the bottleneck might be. I think I am setting all the previous operators correctly (Select Attributes (All), Nominal to Text (Single > Message") and Set Role  (Category > Label)) and then I have a bundle of process operators (Tokenize > Stem Porter > Transform Cases > FilterStopwords) but they are allset to their defaults. 

What am I doing wrong? Many thanks.