Every time I open IE9 I get a popup telling me:
A program on your computer has corrupted your default search provider setting for Internet Explorer.
Internet Explorer has reset this setting to your original search provider, Bing (www.bing.com).
Internet Explorer will now open Search Settings, where you can change this setting or install more search providers.
I cannot change the default search provider in "Manage add-ons". The context menu command "Set as default" does not have any effect.
How can I fix this? Reinstalling IE9 does not help.