A problem about projective texture mapping when using unclamped float texture

I implemented the projective texture mapping successfully using the common float texture, whose scope is [0,1]. Now I want to project an unclamped texture using the NV extension-GL_TEXTURE_RECTANGLE_NV and GL_FLOAT_RGBA32_NV. Thanks for your help, I successfully load all the unclamped textures.
Now because I am using the unclamped float texture, so I will replace tex2Dproj with texRECTproj in the fragment program. But after doing these, I get a wrong result. The result using the clamped float texture and tex2Dproj is correct. Anyone has the experience to do with this problem?

void main(float4 texCoordProj    : TEXCOORD0, 
   out float4 color : COLOR,       
   uniform samplerRECT projectiveMap) 
      // Fetch color from the projective texture 
      color = texRECTproj(projectiveMap, texCoordProj);    

I will appreciate if anyone can give me some detail description about how to use texRECTproj :confused:
Thank you in advance!