Format exception

Question

Dear Programmers, I am doing a database application using MSDE and csharp. I am designing a form where the user can use it when he want to make an invoice, the form and the database is as follows: in the database: auto incremented column - bigint - primary key item # - big int - foreign key invoice # - big int - foreign key item status - varchar quantity - int cost - decimal (precision 18 - scale 2) discount rate - decimal (precision 18 - scale 2) total cost - decimal (precision 18 - scale 2) - auto calculated from a trigger in the form: i used the datagrid but i changed the datagrid table style by code, everything looks clear untill i use numbers with fraction like (20.5, 1.5 ... etc) where i get System.formatexception on sqldataadapter.update() says input string was not in a correct format, this error does not occur for the same numbers when i use the default style. Any help please.