Nero won't convert a 40kHz wav file?

When I resample a 44.1kHz wav file to a 40kHz wav file and then try to
convert this file into a 320kb/s Nero AAC file the program (Nero)
either crashes or refuses to let me do this (dbpoweramp too). But when I resample to 32kHz or even the original 44.1kHz instead then I am able to convert to AAC.

Is there any way I can created a Nero AAC file from a 40kHz wav file?
Now I'm somewhat of a beginner (don't know much about command line
stuff unless you show me in steps how to use them) but I do know how to
use different gui's well.

Thanks!

 

You probably can't encode from a non standard sampling frequency.

I've looked and can't find any reference to 40 KHz being 'standard' in M$oft WAV. Instead most documents say something like:

Good luck...