I keep getting the attached error

What's baffling about it is why a nerd would write such an error with no explanation at all. Does anyone know what it means?
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Other favorites from Microsoft:

"An Unknown File caused an Unspecified Error"

"A Fatal Error has Occured - OK?"

Thanks - rev

I scanned the drive with chkdsk and I got the message 'Scanning and repairing' but nothing told me if there was anything to repair.

There doesn't appear to be an attachment here.

What are you doing when the Error occurs?

Sorry about the attachment. It simply said Explorer.exe with ! next to it.

The error comes up on boot but this time I didn't get it. Maybe the scan and fix actually worked but I'm still curious because it sounds like a boot disk error.