Unable to locate WordPress Plugin directory

I just made a fresh install of WordPress 2.8. As usual, the installatoin process was simple and straight forward. After doing some configurations, I wanted to install some plugins directly using the automatic installer from dashboard. But, I had a problem.
After filling in the FTP information, my WordPress gave me this message:

Unable to locate WordPress Plugin directory

I have no idea about this error. I never got this kind of error. What’s wrong? It seems that some users also found this problem. There’s also an interesting discussion about this. Is it WordPress’ bug? Or, is it related to server configuration? Anyone got this problem too?