your code is similar to the example below minus the Min/Mag filters which shouldn't matter (and i don't think 6 is a valid transparency mode in your code so it'll read it as 0?) :
// set window properties
SetWindowTitle( "TransPlane" )
SetWindowSize( 640,360, 0 )
SetWindowAllowResize( 1 )
// set display properties
SetVirtualResolution( 640,360)
SetOrientationAllowed( 1, 1, 1, 1 )
SetSyncRate( 30, 0 )
SetScissor( 0,0,0,0 )
UseNewDefaultFonts( 1 )
Red = MakeColor(255,0,0)
DrawBox(0,0,63,63,Red,Red,Red,Red,1)
DrawBox(64,64,128,128,Red,Red,Red,Red,1)
Render()
IMG = GetImage(0,0,128,128)
SetImageMinFilter(IMG,0)
SetImageMagFilter(IMG,0)
SetImageWrapU(IMG,1)
SetImageWrapV(IMG,1)
Plane = CreateObjectPlane(256,256)
SetObjectScale(Plane,0.02,0.02,0.02)
SetObjectImage(Plane,IMG,0)
SetObjectUVScale(Plane,0,4,4)
SetObjectTransparency(Plane,1)
SetCameraPosition(1,0,0,0)
SetCameraRotation(1,0,0,0)
MoveCameraLocalZ(1,-10)
do
RotateObjectLocalZ(Plane,1)
If Last# + 1 < Timer()
SetClearColor(Random(0,255),Random(0,255),Random(0,255))
Last# = Timer()
EndIf
If GetRawKeyState(27) then End
Print( ScreenFPS() )
Sync()
loop

otherwise, it might have something to do with your object or image (regardless of it working fine in DBPro) so if it's legal for you to post it, do and we can look at it?