GTA 4 patch error GTA was not detected

Here is quick solution

1. Go to Desktop
2. Right Click and on new option click no NEW TEXT Document.
3. open new text document
4. Copy an paste below  
5. Windows Registry Editor Version 5.00
   
   [HKEY_LOCAL_MACHINE\SOFTWARE\Rockstar Games]
   
   [HKEY_LOCAL_MACHINE\SOFTWARE\Rockstar Games\Grand Theft Auto IV]
   "InstallFolder"="F:\\Rockstar Games\\Grand Theft Auto IV"
   "InstallComplete"="1"
   "INSTALL_LANG"="1031"
   
   [HKEY_LOCAL_MACHINE\SOFTWARE\Rockstar Games\Grand Theft Auto IV\1.00.0000]
   
   [HKEY_LOCAL_MACHINE\SOFTWARE\Rockstar Games\Rockstar Games Social Club]
   "InstallFolder"="C:\\Programme\\Rockstar Games\\Rockstar Games Social Club"
   "InstallLang"=" /clone_wait /L1031 /zAUTORUN"
   
   [HKEY_LOCAL_MACHINE\SOFTWARE\Rockstar Games\Rockstar Games Social Club\1.00.0000]
6. Now in this registries you can change the location  to where you have saved your game here "InstallFolder"="F:\\Rockstar Games\\Grand Theft Auto IV"
7.  now save the file and change its format from .txt to .reg. See here how to do it
   
8.  now go to run option and type regedit 
9. go to registries and click on file and then import 
10. find out your file and improt it. hence you will able to update your registries.