Troubleshooting SQL Error: 18456, Severity: 14, State: 5

In moving my dev system, an odd thing came up. This is usually an easy fix, but for those out there who love their "red herrings", this can throw you, so I hope this helps someone else.

When connecting to the database, I received this error:
Error: 18456, Severity: 14, State: 5.
Login failed for user 'DOMAIN\COMPUTERNAME$'. Reason: Could not find a login matching the name provided. [CLIENT: 127.0.0.1]

Generally, this is as easy as adding the missing account (in this case the local system account) in SQL, giving it the right permissions, and being done. Not so simple sometimes with IIS involved, however.

When looking at the advanced properties of the Default Web Site, I am using an application pool called "DefaultAppPool". Yes, I know - quite creative. This is the account I need to add into SQL and give it proper database permissions.

So a simple SQL command away, and we're done...
CREATE LOGIN [IIS APPPOOL\DefaultAppPool] FROM WINDOWS

Give this account proper permissions to the database, and you're good to go.

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