How do I fix a weird security error on an old local drive?

Context:

I used a hard disk as my Windows installation disk until I finally upgraded to a solid state drive. I now use my old local drive as drive G: for extra storage. I did not format it because it contained valuable data, and I don't have the extra storage (or money) to remove the data, format the disk, and return the data. I will probably do this later if there is no easier solution.

Problem:

Trying to create or paste a file in the root directory of the old local drive results in this error:

Error 0x80070522: A required privilege is not held by the client.

However, I can create or paste a file in any existing folders on the old local drive just fine. After that, I can cut/paste from elsewhere on the drive to the root directory! So there's my workaround. But why am I not allowed to create or paste anything directly in that root directory?

More info:

Windows 7 Home Premium Service Pack 1 64-bit

The security settings for the drive are exactly the same as my two others non-local drives (with minor useless differences with the Users group; I only ever deal with Administrators because this is a one-user computer).

Using chkdsk found no problems. Likewise, Hard Disk Sentinel sees nothing wrong with any of my drives.