How to avoid this problem in emission spectrum calculations?

I've been trying to calculate emission spectrum using this tutorial https://docs.google.com/document/d/1f2LbJMfcudxNjUrrchj8_UEKW8HLDPczRiS2m_2QbzA/pub Instead of spectrum I get this message at...

22 March 2019 7,154 1 View