What does this message mean?

Giganews Newsgroups
Subject: What does this message mean?
Posted by:  c676228 (betty@newsgroup.nospam)
Date: Mon, 24 Aug 2009

Hi all,

In order to create another similar site to one of our existing sites,
I copy all the site files to another folder so I can modify some of the
files  without impacting on the existing site.

After creating the new folder, the following message comes up since
VI_Controls_RuleValidationErrorGroup.ascx will be in both sites' controls'
I don't know what exactly it means. Can you help to decipher?

17    The type 'VI_Controls_RuleValidationErrorGroup' exists
in both 'c:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET
Files\mysite\48f08168\8ce5689c\App_Web_nutcbmwz.dll' and
'c:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET

C:\TFS Projects\Test\Source\mysite\VI\Quote.aspx.cs