D3DDevice.SetRenderTarget Error, Please help.

I've spent hours straight writting a pixel perfect collision detection procedure and when I've came to test it I got an Automation Error when I get to this line:

VB Code:

D3DDevice.SetRenderTarget Sur1

Sur1 is a DirectDrawSurface7 and D3DDevice is declared as Direct3DDevice7.
Is there something I must do to Sur1 before I can set it as the renderTarget? I'm simply trying to paint a D3DSprite to Sur1 which is a tempory dest for the image while I check for collisions.
Am I doing it right, I am ment to set Sur1 as RenderTarget? coz otherwise i'll paint to the Backbuffer.

Thanx for any help.

How are you creating Sur1? There are certain flags you can't have in ddscaps (I think; I haven't done DD in a long time).

VB Code:

Sur1Desc.lFlags = DDSD_CAPS Or DDSD_WIDTH Or DDSD_HEIGHT
            Sur1Desc.ddsCaps.lCaps = DDSCAPS_OFFSCREENPLAIN
            Sur1Desc.lWidth = D1.Right    'Because Left = 0 
            Sur1Desc.lHeight = D1.Bottom  'Because Top = 0 
            
            Set Sur1 = DDraw.CreateSurface(Sur1Desc)

Thanx, that was it, I used this instead and it works fine now:

VB Code:

Sur2Desc.ddsCaps.lCaps = DDSCAPS_3DDEVICE