What is error code -50?

I have been receiving this error code whenever I try to move files to other folders, copy/paste them, or trash them:

"The operation can't be completed because an unexpected error occurred (error code -50)."

I can't empty the trash, either.

Two more problems.

1) I have been getting this message when I try to open certain pages in Safari:

"Safari can't open the page (insert URL here) because the server unexpectedly dropped the connection. This sometimes occurs when the server is busy. Wait for a few minutes, and then try again."

I don't get it for all webpages, though; it's been popping up for Facebook and several Apple-associated sites (like Apple Support). I'm getting a blank white page for Gmail and Twitter, but if I wait long enough they eventually show the previous "unexpected dropped connection" message as well.

I've cleared my cache, gotten rid of cookies, and reset Safari--nothing's been working.

2) Disk Utility is not opening for me. Well, I can see it in my sidebar, but when I click it there is no pop-up with which I can access Disk Utility itself. It says that the application is not responding and I have to Force Quit it.

All three of these problems surfaced today.

My Mid 2009 13" Macbook Pro is running on Mac OS X Lion 10.7.4 with Safari version 5.1.7; I recently replaced my hard drive with an SSD.

Another note: System Information (Apple sign --> About This Mac --> Get More Info) failed to respond when I clicked on the "Storage" tab (not for the others).