I have a site that just recently when trying to add a new event to the Events Module, comes up with the following error:  Please help!

DNN Version: 04.03.07
Events Module Version: 03.02.00

Error: Edit Event is currently unavailable.
DotNetNuke.Services.Exceptions.ModuleLoadException: The Runat attribute must have the value Server. ---> System.Web.HttpParseException: The Runat attribute must have the value Server. ---> System.Web.HttpParseException: The Runat attribute must have the value Server. ---> System.Web.HttpException: The Runat attribute must have the value Server. at System.Web.UI.TemplateParser.ProcessError(String message) at System.Web.UI.TemplateParser.ProcessAttributes(Match match, ParsedAttributeCollection& attribs, Boolean fDirective, String& duplicateAttribute) at System.Web.UI.TemplateParser.ProcessBeginTag(Match match, String inputText) at System.Web.UI.TemplateParser.ParseStringInternal(String text, Encoding fileEncoding) --- End of inner exception stack trace --- at System.Web.UI.TemplateParser.ProcessException(Exception ex) at System.Web.UI.TemplateParser.ParseStringInternal(String text, Encoding fileEncoding) at System.Web.UI.TemplateParser.ParseString(String text, VirtualPath virtualPath, Encoding fileEncoding) --- End of inner exception stack trace --- at System.Web.UI.TemplateParser.ProcessException(Exception ex) at System.Web.UI.TemplateParser.ParseStringInternal(String text, Encoding fileEncoding) at System.Web.UI.TemplateParser.ParseString(String text, VirtualPath virtualPath, Encoding fileEncoding) at System.Web.UI.TemplateParser.ParseFile(String physicalPath, VirtualPath virtualPath) at System.Web.UI.TemplateParser.ParseInternal() at System.Web.UI.TemplateParser.Parse() at System.Web.Compilation.BaseTemplateBuildProvider.get_CodeCompilerType() at System.Web.Compilation.BuildProvider.GetCompilerTypeFromBuildProvider(BuildProvider buildProvider) at System.Web.Compilation.BuildProvidersCompiler.ProcessBuildProviders() at System.Web.Compilation.BuildProvidersCompiler.PerformBuild() at System.Web.Compilation.BuildManager.CompileWebFile(VirtualPath virtualPath) at System.Web.Compilation.BuildManager.GetVPathBuildResultInternal(VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile) at System.Web.Compilation.BuildManager.GetVPathBuildResultWithNoAssert(HttpContext context, VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile) at System.Web.UI.TemplateControl.LoadControl(VirtualPath virtualPath) at System.Web.UI.TemplateControl.LoadControl(String virtualPath) at DotNetNuke.UI.Skins.Skin.InjectModule(Control objPane, ModuleInfo objModule, PortalSettings PortalSettings) --- End of inner exception stack trace ---

I could try that, but my client is wary of upgrading.  Besides, if nothing in the website was changed, why would it suddenly break?

Sounds like this one:
http://www.dotnetnuke.com/Community/Forums/tabid/795/forumid/20/threadid/190664/scope/posts/Default.aspx

More posts in this forum about his issue can be found when searching for "runat".

Reason in short: wrong quotes in runat="server" attribute are not accepted any more by ASP.NET after Windows upgrade.