Permissions are fiddly. Ownership often isn't enough. There are, well, permissions to sort out as well.
The full instructions which will break through any level of ownership/permissions possible are:
Navigate to the file in question, right click on it and select Properties.
Under the Security tab, click Advanced.
Under the Owner tab, click Edit.
Click "Other Users and Groups".
Click Advanced.
Click "Find Now".
Scroll down and double click on Everyone.
Click OK THREE times.
Click on the Permissions tab.
Under type Deny, single click on any entries and click Remove. (N.B.: There may not be any Deny entries, in which case just ignore this step. Just remove any that do exist)
Click OK.
Click Edit (now on the standard file Property window under the Security tab).
Click Add.
Click Advanced.
Click "Find Now".
Scroll down and double click on Everyone.
Click OK.
Single click on Everyone and then tick the "Full Control" box under Allow.
Click OK TWO times.
This is why we created SFCFix. Want a script to do it for you? :)
EDIT: Ooops! You beat me to it!