When you don't have a decimal as number separator the conversion to the excel cell value is not correct.
Current code:
if (typeCode == TypeCode.DateTime)
{
if (stringValue != string.Empty)
{
cell.CellValue = new CellValue() { Text = DateTime.Parse(stringValue).ToOADate().ToString() };
cell.StyleIndex = (UInt32Value)1U;
}
}
Suggested code:
if (typeCode == TypeCode.DateTime)
{
if (!string.IsNullOrWhiteSpace(stringValue))
{
cell.CellValue = new CellValue() { Text = ((DateTime)value).ToOADate().ToString(System.Globalization.CultureInfo.InvariantCulture) };
cell.DataType = new EnumValue(CellValues.Number);
cell.StyleIndex = (UInt32Value)1U;
}
}