I have got the same problem, but apparently not related to encoding and/or character sets. In other words, my passphrase is all numbers and letters only.
The problem for my seems to occur only when I try to use -Dgpg.keyname next to -Dgpg.passphrase. Why do I need to do this ? I have got more than on key in my setup, and I would like to use the non-default one.
Using pgp, I can perfectly well sign any file with the right key using
> gpg --local-user <some-identity> -ab <filename>
Here's my setup re: Maven:
Apache Maven 3.0.2 (r1056850; 2011-01-09 01:58:10+0100)
Java version: 1.5.0_22, vendor: Sun Microsystems Inc.
Java home: C:\dev\java\jdk1.5.0_22\jre
Default locale: de_AT, platform encoding: Cp1252
OS name: "windows 7", version: "6.1", arch: "x86", family: "windows"