This query:

select '1500-02-29' date, DATENAME(dw,'1500-02-29'), DATEPART(dw,'1500-02-29')

results in conversion error ....

Sorry I thought that the script was yours and that it resulted in a conversion error.

Maybe this is my mistake, but then I do not understand this.

To my understanding this is your script.

To my understanding you indicated that it resulted in conversion error.

Sorry, my bad,

Ben