I have two rows of data in several columns. During configuration of two-way ANOVA, why is the Bonferroni post test option greyed out?

Prism doesn't do multiple comparison tests to compare rows, only to compare two columns.

To solve the problem, use Prism's transpose analysis to  flip the table so it has two columns and several rows. Then multiple comparison tests following two-way ANOVA will work. 

Prism version 3 can only compare two columns. Prism 4 and later can handle three or more data set columns.

We've recently added a web calculator that can do other post tests following two-way ANOVA.