SQL Injection Advice.

I've found something that looks like it will take an injection, at work, but I am having trouble figuring out where to go from here.

"http://www.somesite.com/WebService/MemberProfileService.asmx?op=GetOnlineBuddies&profileId=3419&sessionId=d'z"0".

Outputs:

System.Data.SqlClient.SqlException: Cannot insert the value NULL into column 'SITE_FEATURE_USAGETYPESIDFK', table 'SOMESITESecondary.dbo.USER_SESSION_FEATURE_SETTINGS'; column does not allow nulls. INSERT fails.
The statement has been terminated.
at System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection) at System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection) at System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning() at System.Data.SqlClient.TdsParser.Run(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj) at System.Data.SqlClient.SqlDataReader.ConsumeMetaData() at System.Data.SqlClient.SqlDataReader.get_MetaData() at System.Data.SqlClient.SqlCommand.FinishExecuteReader(SqlDataReader ds, RunBehavior runBehavior, String resetOptionsString) at System.Data.SqlClient.SqlCommand.RunExecuteReaderTds(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, Boolean async) at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method, DbAsyncResult result) at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method) at System.Data.SqlClient.SqlCommand.ExecuteReader(CommandBehavior behavior, String method) at System.Data.SqlClient.SqlCommand.ExecuteReader() at ICSSolutions.SOMESITE.Data.NetCommand.ExecuteReader() at ICSSolutions.SOMESITE.Utilities.DataUtilities.DBGetObjects() at ICSSolutions.SOMESITE.Utilities.Security.CheckFeature(String sessionID, SQSiteFeatureTypes feature, Int32 profileID, Int32 userID, Int32& currentUserValue, Int32& maxUserValue, Int32& maxSystemValue, Object objectId) at SOMESITE.WebService.MemberProfileService.GetOnlineBuddies(Int32 profileId, String sessionId)

Any advice would be very appreciated. If I can get it to work one of the bosses will take me out to lunch.

Thanks!