I can only assume that the issue was with the My Sites site collection template ID.
I stumbled across this error when the template it was set to STS#0 on this section where SPSMSITEHOST#0 should be:
I stumbled across this error when the template it was set to STS#0 on this section where SPSMSITEHOST#0 should be:
<WebApplication type="MySiteHost" name="MySite Host" applicationPool="MySites" url="http://mysites" port="80" UseHostHeader="true" AddURLToLocalIntranetZone="true" GrantCurrentUserFullControl="true" useClaims="true" useBasicAuthentication="false" useOnlineWebPartCatalog="false">
<Database>
<Name>Content_MySites</Name>
<DBServer />
<DBAlias Create="false" DBInstance="SERVER\INSTANCE" DBPort="" />
</Database>
<ManagedPaths>
<ManagedPath relativeUrl="personal" explicit="false" />
</ManagedPaths>
<SiteCollections>
<SiteCollection siteUrl="http://mysites" HostNamedSiteCollection="false" Owner="dev\sp2013admin" Name="My Sites" Description="My Sites" SearchUrl="http://localhost/search" CustomTemplate="false" Template="SPSMSITEHOST#0" LCID="1033" Locale="en-us" Time24="false" />
</SiteCollections>
</WebApplication>
Hope this helps.