Macbook Pro wont open apps or download content due to Error Code: -50. My Macbook Pro ran into a problem and reported Error: -50.  I cannot open applications such as Chrome, Word, and others.  I cannot download content or move content to the trash because it says the disk is full, even though it still shows 80Gb of free storage.  The Ram is free and I cannot run ClamXav to see if it is a virus.  Disk Utility verifies the disk but the permissions have all changed and cannot be repaired.  Some permissions errors include "user differs on private/var/at, should be 0 user is 1"as well as various others.  I cant even see/open external drives I connect.  Any idea how to solve this problem?
-50 is a file system error: "Error in user parameter list" (see https://support.apple.com/kb/HT1618)

What OS X version are you on? https://support.apple.com/kb/HT4718 or Will reinstalling Lion erase all my documents and applications? maybe helpful.