I only have this problem when i trie to patch gw2 while using a UMTS Stick.
But i have a work around while the general problem is not fixed.
Step 1: Load all Datas up to 99% (1-3 files remaining)
Step 2: Use a VPN freeware software solution to get a new identity
Step 3: Restart the launcher
" Now you are not connected to gw2 update Servers directly. You will send your request to the VPN Server and this Server will get the Data without problem from the update server and deliver to you. "
Step 4: Shut down the VPN software
Step 5: Enjoy playing GW 2
So it seems that the problem is the conection to the update server, not the client itself. Maybe the last file is stored on a central update server, while all other Datas can be loaded from other Servers and there is a problem with a special DNS Server, so the client can’t connect to this special server?
i hope you excuse my bad english and this solution will help some other players while waiting for a working fix.