Character set and File exists

[bingumalla satyanarayana]

Hello,

I am new to GnuPG. If I run any command from gpg, I am getting the following 
message:

gpg: conversion from `utf-8' to `roman8' not available

I am using HP Unix 11.0. Is there any way to avoid the above message?

Secondly, I am giving -o option in the command line and if the file already 
exists, I am prompted with the following message:

File `b.txt' exists. Overwrite? (y/N)

Is there any option to avoid the above message?

Thanks  in advance for your help.

Thanks,

Satya