'TSubobjectPtr::operator =' : cannot access private member declared in class 'TSubobjectPtr'

'My Code:

UCLASS() 
class AmyCharacter : public ACharacter
{
	GENERATED_UCLASS_BODY()
      ........
}

AmyCharacter::AmyCharacter(const class FPostConstructInitializeProperties& PCIP)
	: Super(PCIP)
{
   Mesh = NULL;//<------ that's the line 43 from myCharacter.cpp
      ........
}

It produce these 2 errors:

Error 1 error C2248:
‘TSubobjectPtr::operator
=’ : cannot access private member declared in class
‘TSubobjectPtr’ D:\Unreal
Projects\FPSProject\Source\FPSProject\myCharacter.cpp 43

Error 2 error C2248:
‘TSubobjectPtr::TSubobjectPtr’
: cannot access private member
declared in class
‘TSubobjectPtr’ D:\Unreal
Projects\FPSProject\Source\FPSProject\myCharacter.cpp 43

So how can i assign a new value to Mesh field ?

Note:
mesh is inherited from
Runtime\Engine\Classes\GameFramework\Character.h

class ENGINE_API ACharacter : public APawn
{
	GENERATED_UCLASS_BODY()

		UPROPERTY(Category = Character, VisibleAnywhere, BlueprintReadOnly)
		TSubobjectPtr<class USkeletalMeshComponent> Mesh;
.......................
}

If you just want to clear it you could do

Mesh.Reset();

yup.i can do anything but assigning any other value.

For example,this also failed with same error:

 FString testSong = TEXT("SkeletalMesh'/Game/GenericMale.GenericMale'");
 static ConstructorHelpers::FObjectFinder myAssetForTP(*testSong);
 if (myAssetForTP.Succeeded())
 Mesh = (USkeletalMeshComponent*)myAssetForTP.Object;

any help with assignment method?

Try

Mesh->SetSkeletalMesh()

yup.that is what i was intended to do.
and it worked.
thanks.
it will save lots of additional tasks which was instructed in c++ fps tutorial.
+it also solved my another issue:
https://answers.unrealengine.com/questions/81518/how-to-change-mesh-value-of-a-character.html

I always use the following trick. Let’s suppose that we have troubling Header.h file with method in private/protected field. I use:

#define class struct
#define private public
#define protected public
#include "Header.h"
#undef class
#undef private
#undef protected