Try these, Helped me when i had same problem
Are you an administrator on your computer or on Windows Vista / 7?
You may need administrator privileges to run the client or properly access the folder in which your game client is located. Try starting Gw2.exe by right-clicking on the file and selecting Run as Administrator.
Is the folder that contains the game set to Read Only?
The client needs to add files to the folder through patching before it will run properly. To check this, right-click on your Guild Wars 2 folder and select Properties. From here, un-check the option for Read-Only and left click on Ok.
Have you updated your video card drivers recently?
AMD users should be using Version 12.3 located here.
Nvidia users should be using Version 296.10 located here.