I'm using my GTA IV Modding Unlocker. It's given me no problems, and shouldn't give you or anybody else any problems.
I don't know why the MagicIV patch messes up you trying to launch your game. The sole purpose of MagicIV is to allow modding, which fails to live up to its intended use.
Anyway, I find it easy if you just use my program with:
An install of GTA IV with no files modded w/applied v126.96.36.199 patch from Rockstar.
Download here: http://www.gtagaming.com/downloads/download/1854
If all your files are in the original state, this patch will work. I'll upload a small "service pack" with all the original files if you want.