Unable to cast object of type ‘System.Linq.Expressions.UnaryExpression’ to type ‘System.Linq.Expressions.MemberExpression’

You need a separate line to extract the Member where the input expression is a Unary Expression.

Just converted this from VB.Net, so might be slightly off – let me know if I need to make any minor tweaks:

public string GetCorrectPropertyName<T>(Expression<Func<T, Object>> expression)
{
    if (expression.Body is MemberExpression) {
        return ((MemberExpression)expression.Body).Member.Name;
    }
    else {
        var op = ((UnaryExpression)expression.Body).Operand;
        return ((MemberExpression)op).Member.Name;
    }                
}

The VB version is:

Public Shared Function GetCorrectPropertyName(Of T) _
             (ByVal expression As Expression(Of Func(Of T, Object))) As String
    If TypeOf expression.Body Is MemberExpression Then
        Return DirectCast(expression.Body, MemberExpression).Member.Name
    Else
        Dim op = (CType(expression.Body, UnaryExpression).Operand)
        Return DirectCast(op, MemberExpression).Member.Name
    End If
End Function

Note that the input expression does not return string necessarily – that constrains you to only reading properties that return strings.