I create a screen to insert and update records of a table using some textboxes and dropdownlists. The new record can be successfully inserted. But have error every time I
want to update the record. Below is exception message.

System.InvalidCastException: Unable to cast object of type 'System.String' to type 'System.Data.IDbCommand'.
   at OakLeaf.MM.Main.Data.mmDataAccessBase.CreateUpdateSelectCommand(DataSet ds, String tableName)
   at OakLeaf.MM.Main.Data.mmDataAccessSql.SaveDataSet(DataSet ds, String tableName, String primaryKeyName, Boolean retrieveAutoIncrementPK, IDbDataAdapter dbAdapter)
   at OakLeaf.MM.Main.Business.mmBusinessObject.SaveDataSet(DataSet ds, String tableName, String databaseKey, IDbDataAdapter dbAdapter)
   at OakLeaf.MM.Main.Business.mmBusinessObject.SaveDataSet(DataSet ds, String tableName, String databaseKey)
   at OakLeaf.MM.Main.Business.mmBusinessObject.SaveDataSet(DataSet ds, String tableName)
   at OakLeaf.MM.Main.Business.mmBusinessObject.SaveDataSet(DataSet ds)
   at OakLeaf.MM.Main.Web.UI.mmBusinessWebPage.Save(mmBusinessObject bizObj, DataSet ds, String tableName)
   at OakLeaf.MM.Main.Web.UI.mmBusinessWebPage.Save(mmBusinessObject bizObj, String tableName)
   at OakLeaf.MM.Main.Web.UI.mmBusinessWebPage.Save(mmBusinessObject bizObj)

I am using MM.Net version 2.1. May I know what is the possible cause of this error?