[VB 6] 2D Engine doensn't Work complete

[P31]

Now this is the 6. Forum where i Ask about my Problem!

I've Programmed a Little 2D Engine that should render a Little Map with BitBlt.
But it doesn't work correct. It doesn't Render Right. Sometimes it forgots big parts and Sometimes it Renders to much!
The Figure you can move shows you the Original Map!
Move with the Figure up until it doesn't Work anymore and you see the end of the map. Move with it Left until it doesn't Work anymore and you see the End of the Map Here!
The Engine should Render an MapData.
It's not Complex. It's constructed like this:

123
456

Every Number is an TextureID
And there is a Matrix. The Cords are:

Numer 1:
X=0
Y=0
Numer2:
X=1
Y=0
Number 3:
X=2
Y=0
Number 4:
X=0
Y=1
Number 5:
X=1
Y=1
Number 6:
X=2
Y=1

So i hope you can help me.

Source Download is here:

http://pprojects.de/filez/2D_Engine.rar

I really hope someone here can help me