This is an error that's a little misleading. At first it might seem that the file is missing or that there is a permissions issue, but that's not the case. The problem is that there is a bad charater in the template file.
Log
Name: Application
Source:
Microsoft-SharePoint Products-SharePoint Foundation
Date:
3/6/2013 1:07:44 PM
Event
ID: 7043
Task Category: Web Controls
Level:
Error
Keywords:
User:
DOMAIN\farm-admin
Computer:
sharepoint-server.domain.local
Description:
Load control template file /_controltemplates/TaxonomyPicker.ascx
failed: Could not load type
'Microsoft.SharePoint.Portal.WebControls.TaxonomyPicker' from assembly
'Microsoft.SharePoint.Portal, Version=14.0.0.0, Culture=neutral,
PublicKeyToken=71e4bce131e9439c'.