The error is very odd. Please download the latest 1.0.2004.2 templates + runtime libraries from the customer area and try again.
(as the property is writable: )
/// <summary>
/// If <see cref="IsIdentity"/> is set to true, this property has to be set to the name of the sequence which supplies the value for the EntityField's
/// corresponding table field. On SqlServer this is @@IDENTITY or SCOPE_IDENTITY() and only used when the row is succesfully inserted, however on Oracle
/// f.e. this value is used to specify a new value and to retrieve the new value. Is undefined when <see cref="IsIdentity"/> is set to false.
/// </summary>
public string IdentityValueSequenceName
{
get { return _identityValueSequenceName; }
set { _identityValueSequenceName = value;}
}