If you are aware of all this, the fix is simple: delete the out-of-date Instant On driver and install the new one. Had I known to check the Rogue Amoeba website, I would have been led to this solution. But how would I know to check? I did try a few Google searches, describing the symptoms, but nothing about Instant On ever appeared in the results.
So, I had to instead use old-fashioned detective work to track down the culprit. As the same technique works for solving a variety of similar problems, you may find it helpful to know what I did.
- I downloaded a fresh copy of Yosemite from the Mac App Store and reinstalled the update. Had the cause of the symptoms been a faulty install, this could have cured my Mac. It did not.
- I restarted via a Safe Boot. This disables login items as well as selected system software. If the symptoms vanished, it would indicate that one of the disabled items was the culprit. The symptoms did not vanish.
- I logged into a test user account. This would tell me if the problem was incompatible software specific to my personal ~/Library folder. The symptoms remained.
- Getting desperate, I installed a clean version of Yosemite onto a spare hard drive and booted from it. This checked if the culprit was anything on my default drive that was not included as part of the new software. If this failed, I was out of routine options. It would indicate some hardware-related issue.
Fortunately, it did not fail. The symptoms disappeared when booted from the clean install. This suggested that the problem was third-party software located either in the /System/Library or (more likely) the /Library folder on my default startup drive.
But how to find out which one of the hundreds of thousands of files in these folders was causing all the havoc? To discover the answer, I turned to tiresome trial-and-error. After making sure I had everything backed up, I removed a half dozen subfolders from the main /Library folder and restarted. If removing the folders had no effect, I would remove an additional group of six folders and restart again. I did this until the symptoms vanished. By doing this, I narrowed the likely cause to one group of six folders.
Now I added back three of the suspect six folders and restarted again. Bingo! The symptoms returned. I kept going with this process of alternately removing files and adding them back, as appropriate, until I determined that InstantOn.driver was the guilty item.
The moral of the story? There are actually two. First, no matter how bad the situation looks, don't despair. There may be a simple and easily fixable cause for your Mac troubles. Second, never underestimate the power of a single item, even an obscure seemingly innocuous one, to cause a world of trouble. Trust me. I have first-hand experience.
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