DataTable dt = (DataTable)Session["name"]; unable to cast

Question

Unable to cast object of type 'System.String' to type 'System.Data.DataTable'.

Please help me how to resolved this error

my code

ctx.TempLedgerBranches.Add(postData);

Session["postData"] = postData;

DataTable mdt = (DataTable)Session["postData"]; error show on this line