1396 - Error: "Failure of Rehydration Service installation may result in inaccurate last access time on files"

Symptom

During a silent installation of the InstantData Service (IDS), a warning is shown to the following effect:

"Failure of Rehydration Service installation may result in inaccurate last access time on files. 
Scanning service will not be affected."

Cause

This warning is the result of IDS failing to save the backup account details when ESE attempts to configure IDS with that account. You will see the following error in the IDS log at the time when ESE tries to configure the backup account:

"An unhandled exception was thrown by the application. System.IO.IOException: The file exists."

IDS attempts to create a temporary file when saving the configuration, but this fails, causing the error. According to this blog post, the error "The file exists" in this case means that C:\Windows\Temp has more than 65 535 files in it, and needs to be cleared.

Solution

1. Clear out C:\Windows\Temp.
2. Investigate how the directory was filled in this way, and address the cause to prevent future issues.