このエラーの原因がわかりません。コードを確認する必要がある場合は、default.aspx に関連付けられている MasterPage.master を教えてください。
これは、ブラウザで表示されるエラーです。
Server Error in '/WebSite1' Application.
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Content controls have to be top-level controls in a content page or a nested master page that references a master page.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.
Exception Details: System.Web.HttpException: Content controls have to be top-level controls in a content page or a nested master page that references a master page.
Source Error:
An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.
Stack Trace:
[HttpException (0x80004005): Content controls have to be top-level controls in a content page or a nested master page that references a master page.]
System.Web.UI.MasterPage.CreateMaster(TemplateControl owner, HttpContext context, VirtualPath masterPageFile, IDictionary contentTemplateCollection) +8690104
System.Web.UI.Page.get_Master() +51
System.Web.UI.Page.ApplyMasterPage() +15
System.Web.UI.Page.PerformPreInit() +45
System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +282
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Version Information: Microsoft .NET Framework Version:2.0.50727.5466; ASP.NET Version:2.0.50727.5456