Right click on the drive where your files/folders are located.
Select Properties.
Navigate to the Security tab.
Local Disk Properties (Security)
Click Advanced and then select Change permissions.
Select change permissions
Highlight your user and then click Edit.
Highlight your user and click Edit
Select This folder, subfolders and files from the drop-down list.
Check the Full Control box under Basic Permissions.
Check the Full Control Box
Click OK.
Then go to your GTA IV main folder
Right click on the folder and uncheck Read only mode
Apply