RyWilson

okay i was looking up other things in anticipation of that not working. there are MANY people who have had this exact error but they are all solved differently. i will include a few of them to see which problem you are most likely having.
the only way you will be able to find which is for you is to try them until yours is fixed. i would recommend making a backup copy of your game while you try these because im guessing it might not be as easy as these people say :P a few of them have said that error means something is missing or corrupt. so its a guessing game at this point.
http://gtaforums.com/topic/445459-fatal-error-rmn60-gtaiv/
see if this helps at all. i was on Steam looking up the problem as well and again many different solutions.
 

your specs look fine. since it seems like it might be very simple to fix. the easiest and simplest thing is to try launching GTA IV as administrator. if that doesn't seem to get you anywhere get back to us. we'll go step by step :)

it probably has to do with the advanced hook in the els folder. The one that comes with lcdpfr is newer. My advice is re install lcdpfr then u SHOULD be set :P

OK so are you able to pull over cars now? Be sure you are close enough and it prompts you to exit your vehicle before you get out. If not the suspect drives off and you gotta start the stop over

you can play the GTA IV game just by starting it. the actual LCPDFR mod won't factor in until you press Alt P (this works to go on duty as well as go off duty and return to normal game) so if you just wanna play the GTA IV game you put the disc in and start like you normally would and forget about the police mod even being there. at ANY time you are ready to become a cop, press Alt P and report to a station for duty.
 
Remember if this helps your problem please mark best answer so they can close this thread :D