I am having the same problem. I have one database that gives the error, "This action cannot be performed because this file is not modifiable". But the permissions are R/W, the account I'm using has full privileges. Other files on the same server don't have this problem. The only thing weird about the File Info is that the "Locked" checkbox is greyed out, which I've never seen before. Also, on this file, and also files that open fine, instead of listing all the users with access, some of them just show "Fetching..."
I'm guessing that you are putting your files in "Program files" folder under windows operation system?
The problem is windows itself during installation it makes some of runtime files (mostly common USR files) unwritable. That's why probably you cannot create new records and all other weird things inside Runtime solution.
Try to install it on other location or simply (if all your clients have access to Admin account in Windows....) - run as administrator. That will solve it in a simple way.
Maybe someone with grater experience has some other solution... please feel free to describe.
No this is not a Windows problem, but a Mac problem.
In instruct my Windows users to install in the root C:/ drive which usually causes no issues... usually.
But the 'file not modifiable error' sometimes occurs on Macs (does not matter which OS X version). The runtime is codesigned properly. Again, only some Macs, which is odd. As mentioned earlier, usually a Disk Permissions Repair fixed this issue, but the only solution I have found that guarantees the proper launch if this occurs is a reinstall of the OS.