Input String not in correct format

I'm not sure what to look for next. I receive an error 'Input string is not in the correct format'. It's on the intqty variable.
If I hard code a 2 inplace of the Convert.ToInt32(gvOP.Rows(i).Cells(0).Text)
it will work.
What am I doing wrong here?
Dim intqty As Integer = Convert.ToInt32(gvOP.Rows(i).Cells(0).Text)
 
Protected Sub btnRecalc_Click(ByVal sender As Object, ByVal e As System.EventArgs)
        Try
            If Me.gvOP.Rows.Count > 0 Then
            &nbs ...