@KaneJr Is your copy the steam version of GTA? I had the same problem which I figured out after some fiddling around.
I have two GTA V folders on my computer, the original unmodded "Grand Theft Auto V" folder installed from steam and then a folder I created named "Grand Theft Auto V - MODDED" to which I copied all of the contents and files from the "Grand Theft Auto V" folder. This way I could play both online with my friends using the clean GTA folder and play with mods like LSPDFR without risking a ban from online by using the alternate modded folder.
Now, when I tried to run RPH from the "Grand Theft Auto V - MODDED" folder I got the same problem @KaneJr is describing, where RPH fails to hook the game. How I resolved the problem was by moving my modded install into the "Grand Theft Auto V" folder and then everything worked flawlessly. Before that I did create a third folder named "Grand Theft Auto V - ORIGINAL" to which I moved the unmodded contents of the "Grand Theft Auto V" folder. This way I can still choose whether I want to play modded or unmodded by dragging the contents from either "Grand Theft Auto V - MODDED" or "Grand Theft Auto V - ORIGINAL" into the "Grand Theft Auto V" folder.
Sorry for the mess that was that info dump but hopefully this can be of some kind of service. This three-folder system is working great for me especially as I can just select everything in the original or modded folders, cut, and paste the contents in steam's GTA V folder and be good to go.