Error while doing an Insert in a formview via ObjectDataSource

Hi!
I am making a website for a movie theatre. Registered Users can add a review to a movie. I am doing this through a FormView with an ObjectDataSource.
Anyways, when i run this the page loads, but as soon as I click the 'Add' button I get the following error, I don't even get in my code behind. Any Ideas? Thanks in advance.
Index was outside the bounds of the array.
[IndexOutOfRangeException: Index was outside the bounds of the array.] System.ComponentModel.BaseNumberConverter.ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, Object value) +415 [Exception: is not a valid value for Int32.] System.ComponentModel.BaseNumberConverter.ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, Ob ...