i.n.c.AbstractChannel$AnnotatedSocketException: cannot assign

I have below simulation setup in place for REST API (/POST).

    svcScn.inject(constantUsersPerSec(*500*) during (*60* minutes))
        reachRps(*500*) in (*20* seconds),
        holdFor(*60* minutes)
    .maxDuration(*65* minutes)

10% of the http requests are getting above error. Not sure if its rest api specific error or some network config tweak would help.

Anybody encountered this before?