problem with aspnet_users

Hello,

I hope this is the right place to ask my question. I'm making an website as project for school it is ment to help students learn and practice physics. i wanted some additional info stored with the user data like in witch year the student is and wether or not he ad practiced a specified toppic. when u want to edit the gridview (in internet explorer) it gives the following error:

Server Error in '/pws_web' Application.

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Implicit conversion from data type sql_variant to uniqueidentifier is not allowed. Use the CONVERT function to run this query.

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.Data.SqlClient.SqlException: Implicit conversion from data type sql_variant to uniqueidentifier is not allowed. Use the CONVERT function to run this query.

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:

[SqlException (0x80131904): Implicit conversion from data type sql_variant to uniqueidentifier is not allowed. Use the CONVERT function to run this query.] System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection) +177 System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection) +68 System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj) +199 System.Data.SqlClient.TdsParser.Run(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj) +2305 System.Data.SqlClient.SqlCommand.FinishExecuteReader(SqlDataReader ds, RunBehavior runBehavior, String resetOptionsString) +147 System.Data.SqlClient.SqlCommand.RunExecuteReaderTds(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, Boolean async) +1021 System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method, DbAsyncResult result) +314 System.Data.SqlClient.SqlCommand.InternalExecuteNonQuery(DbAsyncResult result, String methodName, Boolean sendToPipe) +413 System.Data.SqlClient.SqlCommand.ExecuteNonQuery() +115 System.Web.UI.WebControls.SqlDataSourceView.ExecuteDbCommand(DbCommand command, DataSourceOperation operation) +392 System.Web.UI.WebControls.SqlDataSourceView.ExecuteUpdate(IDictionary keys, IDictionary values, IDictionary oldValues) +643 System.Web.UI.DataSourceView.Update(IDictionary keys, IDictionary values, IDictionary oldValues, DataSourceViewOperationCallback callback) +78 System.Web.UI.WebControls.GridView.HandleUpdate(GridViewRow row, Int32 rowIndex, Boolean causesValidation) +1218 System.Web.UI.WebControls.GridView.HandleEvent(EventArgs e, Boolean causesValidation, String validationGroup) +853 System.Web.UI.WebControls.GridView.OnBubbleEvent(Object source, EventArgs e) +87 System.Web.UI.Control.RaiseBubbleEvent(Object source, EventArgs args) +35 System.Web.UI.WebControls.GridViewRow.OnBubbleEvent(Object source, EventArgs e) +117 System.Web.UI.Control.RaiseBubbleEvent(Object source, EventArgs args) +35 System.Web.UI.WebControls.LinkButton.OnCommand(CommandEventArgs e) +86 System.Web.UI.WebControls.LinkButton.RaisePostBackEvent(String eventArgument) +153 System.Web.UI.WebControls.LinkButton.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) +7 System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +11 System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) +172 System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +4921

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Version Information: Microsoft .NET Framework Version:2.0.50727.42; ASP.NET Version:2.0.50727.42

I'm glad with every sugestion

Wrong datatype.

As a side note, that's what the profile system is for.