Issue 1. Evidently your 11.04 isn't standard any more ( and might be
related to issue 2 below ) so the upgrade cannot work. Trying to force
the upgrade will more than likely break Ubuntu so I'd recommend you do
not continue trying to do the upgrade to 11.10 - if you really want to
use it then a clean install is needed, with all that entails.

Issue 2. Amvis is a mail virus scanner and is pretty old, the last
'news' for it on Sourceforge was in 2004 !!! I'd suggest removing it
using Synaptic Package Manager and choosing the 'Complete Removal'
option. If you want to scan e-mail for viruses then there are up to
date packages that can do this but unless you are sharing e-mail with
Windows users then this really isn't necessary - the Windows user will
have their own AV scanner ( or at least, *should* have ).