Problem: Map Service cannot access cache tiles when using the REST API
Cached map services do not display when using the REST API, but appear in clients making an Internet (SOAP) or Local (DCOM) connection to ArcGIS Server.
The HTTP response code that correlates to the failed request is 404, as it can find the host, but not the file.
The cache tiles are stored on a server that is separate from the Web Server, and authentication issues do not allow the REST tile handler to access the file on disk.
Solution or Workaround
The workflow outlined in ESRI Knowledge Base article 36887 resolves this problem by changing how the request authenticates to retrieve the tiles from the file system. This solution is also a general best practice when configuring ArcGIS Server, and helps to improve the overall performance.
The Identity used in the article is the ArcGISWebServices account, which also needs to have at least read permissions to the cache tiles as well. When using local accounts, the ArcGISWebServices user needs to be created with the same password on the server hosting the cache tiles.
If the ArcGISWebServices user does not have proper file permissions to the cache location, it may take several hours for Windows to apply permissions to the many files contained in the directory.