Tamura (1992) Distance Could Not Be Computed

For one or more pairs of sequences, the Tajima-Nei correction could not be applied. This usually occurs if the argument in the log term of the formula becomes too close to zero or if it is negative, or if the G+C-content is 0% or 100%. If you wish to know which pair(s) of sequences has this problem, use the Distances|Pairwise option. All such pairs will be shown in the Distance Matrix Dialog with a red n/c (not computable).