Can't open guildwars after new build available?

As the title suggests, can't open guildwars after the patch a few minutes ago. The serious error message appears everytime i attempt to launch guildwars.

Anyone else experiencing this problem?

EDIT- The description appearing is :

*--> Crash <--*
Assertion: Unable to write patch file 'C:\Program Files\Guild Wars\Gw.000'
OsPatch.cpp(375)
App: Gw.exe
ProgramId: 1
Build: 29800
When: 3/26/2010 22:26:22
Flags: 0

Have you checked to see if you have available disk space? Just a thought...

Yeah 200GB free. Thanks for trying though.

Still can't open, was running fine all day until this new build update described on guildwars.com as :

Update - Friday, March 26, 2010
Bug Fixes

* Fixed a timing issue with the upcoming weekend event.

Serious error message still appearing!

Try re-booting your computer. I've had the problem before and re-booting solved it for me. Good luck!

Nope no problems here only thing changed was I found an extra stack of ectos in my account storage after the update. )

This happened to me right when the new build was available also. All I did to fix it was right clicking the GW icon than went to properties-compatibility and checked Run as administrator than apply-ok. Should work fine after this aslong as you open it through this shortcut you edited.

If what Boberta said doesn't work then just go to the guildwars website and download the client from there. After the initial part is downloaded and you run it you will need to select the "Reinstall Guild Wars to it's current location" option. This should only take 2 to 5 minutes at most to do and finish. I've gotten the same problem a few times in the past and this is what I did to fix it. I never really felt the need to look into the cause of it because of how easy it is to fix.

Thanks guys rebooting seemed to work.
Wierd never had to reboot for the update to work.

This happens to me all the time when a new build downloads. I always have to re-boot my computer to get the game to run.