It does work though, albeit slowly! I imagine that the processing time is heavily dependent on the computing power available to you. Here are the statistics from my machine (windows 10 64 bit, AMD FX6350 (6 core), 16 GB RAM and AMD Radeon R7 200 series graphics card). I created a LUT from AP at maximum export detail level of 126x126x126 which gives a file of 51.5MB. It takes 12 seconds to load and process the file. AP will also use the graphics processor and any (and sometimes all!) available memory. If your machine is taking minutes to load it, then probably you're running into memory/processor (or just possibly graphics processor) limits. If your machine is 32 bits then you should consider upgrading.
Ok, guys thank you for the help. I figured it out by myself.
I created some more test luts, to recreate the problem, and I just remembered that I was dumb enough to call the LUT something like autumn 1.0 and the (.) messed up the file format...