LCPDFR and the Scripthook are not compatible with the recent unexpected GTA IV update. To make use of script modfications and LCPDFR again, we've compiled the following tutorial that will downgrade you to 18.104.22.168, the last version of GTA IV supported by the Scripthook.
This tutorial will work with GTA IV and GTA EFLC.
First, in your GTA directory, rename paul.dll to paul.original.dll.
Go to this Rockstar support page and download the patch. GTA IV: https://support.rockstargames.com/hc/en-us/articles/200145406--May-28-2010-Grand-Theft-Auto-IV-Patch-7-Title-Update-v-1-0-7-0-English-1-0-6-1-Russian-1-0-5-2-Japanese- GTA EFLC: https://support.rockstargames.com/hc/en-us/articles/200145386-Grand-Theft-Auto-Episodes-from-Liberty-City-Title-Update-1-1-2-0-Patch-2-
Extract the ZIP file to a new folder somewhere in your computer and run UpdateTitle.exe or (EFLC) setup.exe.
After patching is complete, rename paul.dll to paul.old.dll.
Rename paul.original.dll to paul.dll.
Launch GTA IV. If all has went well, your GTA IV has been downgraded.