Dear Freinds

I face a problem with coding which i put in my datagridview

coding is

Dim dis As Integer 
For abc = 0 To counter - 1 
dis = DataGridView1.Rows(abc).Cells(3).Value * DataGridView1.Rows(abc).Cells(4).Value / 100 
Next 
DataGridView1.Rows(abc).Cells(5).Value = dis

its work 1st time when i load the programme correctly but when i entered data again on previously run programme it gives error that "conversion from string to "to double" is invalid "

kindly help me about these error thanks

Maybe the contents of one of the cells is not a number. Or maybe it is a number, but also contains a comma or some non-numerical character.

On which line exactly does the error occur?