BA II Plus - Error 4 message, question, examples, happening, calculator

bleach

i was attempting to go through some quant examples with my calculator and got an error 4 message on my BA II Plus calculator. the example was from stalla SS3 page 8 (covariance coefficient). can anyone please advise why this is happening? i've re-input the data just to make sure that wasn't the cause, but i still have the same error. i've asked the question to stalla, but i'm still waiting for a response.