Recently, my Visual Studio 2008(with Resharper 4.5) has started to reformat asp tags into lowercase.
Example:
Go to Tools | Options...
Expand: Text Editor - HTML
Select the "Format" node, and see what settings you have for "Capitalization" of "Server tag" and "Server attributes - I think the default is now "Lowercase" - try setting that to "Assmebly definition" instead.
More information on these options can be found here:
Format, HTML, Text Editor, Options Dialog Box