I logged in as a portal admin and can execute a web part on Top Portal, but I get the following error when I execute the web part in sub areas ( Topics, News etc).

Please suggest to fix this problem.

System.UnauthorizedAccessException: Access is denied. at Microsoft.SharePoint.g.a(UnauthorizedAccessException A_0) at Microsoft.SharePoint.Library.a.a(String A_0, String A_1, String A_2, Boolean A_3, UInt32 A_4, String A_5, Int32 A_6, Int32 A_7, Boolean A_8, Int32 A_9) at Microsoft.SharePoint.SPAlertCollection.Add(SPList list, SPEventType lEventType, SPAlertFrequency lAlertFreq) at AlertWP.AlertWP.addAlert_Click(Object sender, EventArgs e)