GetProperty reflection results in "Ambiguous match found" on new property

Kevin already pointed out the issue, but you don't need complex statements, or LINQ for that:

PropertyInfo propInfoSrcObj = myDE.GetType().
    GetProperty("MyEntity", typeof(MyDerivedEntity));

The ambiguity occurs because of the new declaration in MyDerivedEntity. To overcome this you can use LINQ:

var type = myObject.GetType();
var colName = "MyEntity";
var all = type.GetProperties().Where(x => x.Name == colName);
var info = all.FirstOrDefault(x => x.DeclaringType == type) ?? all.First();

This will grab the property out of the derived type if it exists, otherwise the base. This can easily be flip-flopped if needed.

Type.GetProperty

Situations in which AmbiguousMatchException occurs ...

...derived type declares a property that hides an inherited property with the same name, by using the new modifier

If you run the following

var properties = myDE.GetType().GetProperties().Where(p => p.Name == "MyEntity");

you will see that two PropertyInfo objects are returned. One for MyBaseEntity and one for MyDerivedEntity. That is why you are receiving the Ambiguous match found error.

You can get the PropertyInfo for MyDerivedEntity like this:

PropertyInfo propInfoSrcObj = myDE.GetType().GetProperties().Single(p => 
    p.Name == "MyEntity" && p.PropertyType == typeof(MyDerivedEntity));

For property:

MemberInfo property = myDE.GetProperty(
    "MyEntity",
    BindingFlags.Instance | BindingFlags.Public | BindingFlags.DeclaredOnly);

For method:

MemberInfo method = typeof(String).GetMethod(
    "ToString",
    BindingFlags.Instance | BindingFlags.Public | BindingFlags.DeclaredOnly,
    null,
    new Type[] { },// Method ToString() without parameters
    null);

BindingFlags.DeclaredOnly - Specifies that only members declared at the level of the supplied type's hierarchy should be considered. Inherited members are not considered.