Anil Singh:
There was some issue related to location of .wav files , So we have changed path of .wav files under defect "CSCtu21705" and changes available in 8.5.1ES78. The error "java.io.IOException" you are getting seems as related to file input/output at given path.
So, can you share diag_tomcat log file to debug this issue, before that please enable VMREST traces.
In the meantime i will also try on 8.5.1ES47 build in our lab and let you know. At current build i am not able to get any error.
-Anil Singh
I am not sure, if its related to the defect as I am able to add the voice name for a user using the said API but its a PUT request not a POST. Try executing a PUT request on the same setup, if it still fails then we can have a webex session to debug the issue further.