Unable to download patch WOTLK Server

So my friend and i just downlaoded the WOTLK application for warmane. Got to the loading screen, put our credentials in, and it said the application needed an update and to restart. Hit restart, install the update, then this message appears. Not sure where to go with the file or what to do. Tried deleting it, help?! :) thank you.

"The file "D:\World of Warcraft 3.3.5a (no install)\WoW.exe" is read only and cannot be overwritten. Please try installing to a different location. (ConflictManager::DeleteFile)"

Log in with your username (not email). If your client files have been modified you should redownload the client.