Post some details about the hdd type.
The steam folder might not have the correct file write-permission in the first place and that happens on alot of hdd types.
It is known that for most steam users:
Steam itself exposes a critical vulnerability in changing folder permissions of its \Program Files\Steam directory, allowing all unprivileged users to replace, modify and/or remove Steams core binaries.
So, most likely, your problem remains: that folder permission changing isn't properly done.
You can also try this small registry tweak to take ownership rights to the steam folder:
Take Ownership (For Vista / Win7, don't even ask about the old XP)
What is does is:
"Taking ownership of a file/directory gives you direct read/write access to the file (without going through UAC) and forces other users to go through UAC to get such access. Now that Vista finally has a sane notion of file ownership (like Linux and Mac have had for years), this sort of thing comes in major handy (especially when you often change files like C:\WINDOWS\system32\drivers\etc\HOSTS)" (
source)