Well their is a way around but you'll need to use paint or some other program that can edit the .png files.
As previously stated by BOOMZ the issue is due to Addtional pipes, the reason being is Addtional pipes contains a file called block_textures_override.png. This file appears to be overriding (or conflicting if you will) with the pipe textures for this mod, there is a way around but it requires some copy & pasting of images in the files.
First off open Energy Coupler's mod file, goto your mods folder and open ( In your case the file name may be different if you changed it) zEnergyCoupler-0.21.1-Client.zip, within the archive goto:
Now look in the bottom right hand corner of the BlockTextures.png file see the three sprites? copy those three, we will need to place them into another file.
Next, while still in the mods folder, open the offending file (In your case the file name may be different if you changed it) zAddtionalPipes.zip, within the archive goto:
Open the file, now paste the sprites we copied in the lower right hand corner of the file (The same position from which you copied them from). Save and enjoy =)
That is very strange, because I use the Additional Pipes mod myself. I even had it installed in my test environment and I did not encounter this texture problem.