Diagnosis
With the calculation of a seasonal index, either the maximum valueof 99.99 was exceeded, or it fell short of the minimum value of 0(negative seasonal index). Both cases can also occur repeatedly.In addition, it is possible that both excesses and shortfalls werefound. In these cases, the values 0 or 99.99 are set by the system.

Procedure
Check the choice of forecast model. If sporadic past developmentexists, an average model may be more suited.