Error when making an anova

I'm doing some anova tests, and they all work out for me, except one. I get this error.

boxplot (Grams.Oils.Consumed ~ Period)
Error in x [floor (d)] + x [ceiling (d)]:
non-numeric argument to binary operator

In all the other groups I had no problem, only in this one.

Can you help me, please?

Hi! It seems that your output variable is of type character, which aov() does not allow. Does changing that variable to numeric solve the issue?