Macbook Pro wont open apps or download content due to Error Code: -50. [duplicate]
Solution 1:
-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.