The problem only happens when running Photoshop CC (2104) and Bridge (actually these are the only two programs I really use my external drive for) during a save or write operation to an external hard drive. I can work for hours, with multiple files open, saving, creating, etc. without a problem and then suddenly I'll get a message from Photoshop saying, "Could not save .... because of a disk error." or from Bridge saying, ".. unable to write to cache..".
When I quit and try to troubleshoot the problem, I find that, for some reason, Mavericks has put system files on my external (non boot) drive or, for whatever reason, thinks there is a system file on it. Consequently, the drive cannot be ejected (Error message: "... one or more programs may be using it...") and I cannot repair it using Disk Utility (Error message: " ... live file system repair is not supported"). I also cannot write to it (Error message: "... unexpected disk error has occurred (error code: -50)"). The problem persists even after quitting all other programs, which wouldn't surprise me if Mavericks thinks there is a system file on it.
I have force ejected the drive a couple of times but became concerned that I might be compounding the problem. Now I just restart my computer and run Disk Utility Repair Disk. (Don't know which is worse.) Disk Utility either doesn't find a problem or, if it finds one, it repairs it. After that, Photoshop and Bridge work fine for a while.
MacBook Pro 13" 2.4GHz with 16GB RAM, 500 GB HD (recently upgraded)
Apple Cinema Display
Mavericks (up to date)
G-Technology G-Drive (Gen 5) 2TB HD connected via Firewire 800 (latest firmware)
Unconfirmed observation: I believe the first few times this problem occurred, Firefox was up an running. I made a point of quitting all programs except System Monitor when running Photoshop and Bridge and I can't remember having the problem again. The the last time the issue occurred, today, however, Safari was up and running.
Is this an OS problem, a hardware (disk drive, cable, etc.) problem, a software problem (PS, Bridge) or some combination? I have put this much detail in the post hoping someone can share some insight into the cause. I will be sending this report to Apple and G-Technology and I will report any resolution, if and, hopefully when, I find one.
The only thing that will cause a disk error is an actual error from the disk.
Photoshop is just telling you what that OS told it about the error.
It sounds like you need to boot off another disk and try to repair your disk.
Also, make sure you have a backup. And check the SMART status to see if it is failing and needs to be replaced.