Error -50 OSX may encountered by the Mac users while accessing or proceeding data from external hard drive. This particular error issue is mostly cased due to use of unsupported correctors in the file name such as @,#,$,%,^ etc. and can be resolved by simply renaming your files. Well, in case if the error still persist even after renaming your files then it clearly reflects that there is some kind of sever corruption in either your external hard drive or files. Anyway, there is no need to worry about as you can still fix Error -50 OSX by using bellow mentioned methods.
Reconnect your External HD :- Sometimes it has been seen that the minor external hard drive problems simply gets resolved by just reconnecting the hard drive properly. Hence, you should unmount your external drive and then mount it properly to check wether the problem resolved or not.
Disk Utility :- Disk Utlity is a built in feature for Mac OS X users that can be used to fix any minor corruption issue related with your Mac machine. You should run the Disk Utility first aid feature in order to try and resolve Error -50 OSX issues completely on your Mac.
In case if none of the manual option works effectively enough to fix this very issue then in such circumstances you will have to format your external hard drive. Formatting will wipes your entire hard drive completely and resolves all kind of corruption problems including this very error. Well, as far as the matter of your lost data is concern you can easily restore all your files by using Mac Data Recovery Software even after Error -50 OSX issue.