The Point Solar Radiation tool will sometimes fail with error 999998, when using a small skysize value.
The skysize value is too small, and needs to be increased.
A value of 200 is default and is sufficient for entire digital elevation models (DEM) with large day intervals (greater than 14 days). A skysize value of 512 is sufficient for calculations at point locations where calculation time is less of an issue. At smaller day intervals (less than 14 days), it is recommended that higher values be used. For calculations of the whole year with monthly intervals, the day interval is disabled and the program internally uses calendar month intervals. The default value is 14.