See this page for the dll and how to install it
The directions are as follows:
To support different languages and character sets, Microsoft Windows
versions of GnuPG make use of a DLL called "iconv.dll". This DLL has
been written by the GNU project too and is used by several
applications ported from GNU/Linux to MS Windows systems. If this
library has not yet been installed on your system, an error message
might have you taken to this page. Please follow the instructions
below to install this library.
GnuPG has a fallback mechanism to work even without this DLL. However
some texts may not show up correclty and when creating a new key it
might not be encoded correctly. Thus unless you are using the Latin-1
or UTF-8 character set, you should definitley install the DLL before
you create a new key or add a new user ID to a key.
If you have used the Gpgwin package to install GnupG, you should never
see this message because this DLL will get installed. However, it
might happen that such a DLL has been insatlled on your system by
another application and later be deinstalled. To rectify this, simply
re-install Gpg4win and your are done.
The DLL is available as a ZIP file at the address
ftp://ftp.gnupg.org/gcrypt/binary/libiconv-1.9.1.dll.zip. You should
also get the corresponding ".sig" file and verify the integrity . This
DLL has been built from the source package libiconv-1.9.1.tar.gz
available at the same FTP sites. We distribute it separately for
convenience and because GnuPG only requires this DLL and not the other
files from the binary package. For copying conditions see the included
To install this DLL, unzip it and copy the file "iconv.dll" to a
directory where you usually keep DLLs. If you don't know such a
directory, it is safe to copy it into the same directory as the
"gpg.exe" file is stored.