Exception attempting to ApplyWebTemplate to SPSite (executing PowerShell)

I am running a basic PowerShell command:

New-SPSite -url $siteCollection -OwnerAlias $siteOwner -Template "STS#0"

For some reason, I am getting the following error:

"Exception attempting to ApplyWebTemplate to SPSite"

The error is being raised because the site template (STS#0) cannot be found. If I substitue STS#0 with any other templates, I get the same error... Also, I can run this same command against existing web applications and it works fine. The issue seems to be happening on newly created web applications.

Anyone seen this before? Does my web app not have something activated/enabled?

Thanks.