Cannot change photo with Yahoo account

I have contacted Yahoo via email about the problem below several times, and all I get back is the same form letter that is totally useless. So I thought I'd try here.

I have a free account with Yahoo. Among other things, you can add a photo to your profile. For the past month or so, Yahoo is not permitting me to do this. I have another computer with a different Yahoo profile and have encountered the same problem. When I try to upload an image to Yahoo from my hard drive, I get this message:

***Sorry, Unable to process request at this time -- error 999. Unfortunately we are unable to process your request at this time. This error is usually temporary. Please try again later. If you continue to experience this error, it may be caused by one of the following: * You may want to scan your system for spyware and viruses, as they may interfere with your ability to connect to Yahoo!. For detailed information on spyware and virus protection, please visit the Yahoo! Security Center. * This problem may be due to unusual network activity coming from your Internet Service Provider. We recommend that you report this problem to them. While this error is usually temporary, if it continues and the above solutions don't resolve your problem, please let us know.***

I don't have spyware or viruses on my PC, and I can log onto Yahoo websites just fine. In fact, I can change any feature of my Yahoo profile except the photo. If I try to use an image from Yahoo's own gallery for my picture, I get this message:

***Restricted Access Sorry! You cannot access this account, as you are not the owner.***

Well, obviously I am the owner because I log in and out of this account all the time. Any suggestions?