Make sure you use EJS to open the xml source and re-compile to generate new jar file again.

The message is just let you know that you have upload the same jar filename before.
It is a warning message:
It is fine if you really want to replace the previous file.

It is a reminder such that you would not over-write something you have created before (old jar file with the same filename will be replaced with new uploaded jar file)

I check out the jar file you have uploaded last time.

It was ejs_Blackbody_Radiation_Spectrum.jar
However, the xml file in the jar file is BlackbodyRadiationSpectrum.xml
So the output of the jar file should be ejs_BlackbodyRadiationSpectrum.jar
Why you change it to ejs_Blackbody_Radiation_Spectrum.jar ???

If the xml source is Blackbody_Radiation_Spectrum.xml than the ejs generated jar file will be ejs_Blackbody_Radiation_Spectrum.jar

However, your ejs source is BlackbodyRadiationSpectrum.xml, the generated jar file by ejs should be
ejs_BlackbodyRadiationSpectrum.jar

And please do not use space " " as part of EJS source.