I did examine every line of code and read the relevent perldocs. In the end the error was that I wasn't using curly brackets but not on the line claiming the error. Until I discovered any false clause caused the error, everything appeared that that an array ref was suddenly not being an array ref. I knew it had to be something I did but when the line claiming to give the error was fine and the perldocs agreed with it, I was at a bit of a loss.