Quite a while ago I ran into the issue where I couldn’t remove code snippets from VS. It seems that is not enough (using the hard way) with removing the registry key (that’s it: HKLMSoftwareMicrosoftVisualStudio8.0LanguagesCodeExpansionsCSharp[PathToYourSnippet]) and the proper snippet file.
To do that you should also remove the snippet from the ExpansionsXML.xml file. If you’re using XP you will find this file here:
c:documents and settings[YOUR USER]Local SettingsApplication DataMicrosoftVisualStudio8.01033
Although if you’re running on vista, you will find it here:
Unafortunately I sent this bug to product feedback but they close the bug.
Another thread where the issue is discussed: