Visual Studio 2005 design time kept giving me the specified error because of the resource files I have been using. (and not using)
The setting of the default culture was being done by the application config. But since in design time you can not read values from your web.config, error occured.
To prevent this, I added a neutral resource to the resources folder with no culturename like : Userinterface.resx (all the others had names like Userinterface.en-CA.resx)
Also you can set a static default culture in your code as well.
Then everything started working. Give it a try befıre panicing about how different Visual Studio 2005 works.