Moss 2007 - Excel Services no file permissions message

 If you receive the following Exception when you try to open the sample workbook or another workbook try the following steps:

You do not have permissions to open this file on Excel Services.Make sure that the file is in an Excel Services trusted location and that you have access to the file.

1.Open Central Administration -> go to Operations tab -Ensure that the Excel Service is running.
2.Open Central Administration -> go to your configured Shared Service -> click Excel Service Settings.

-File Access Method: ensure that it is not using Impersonation, instead the Option Process Account should be enabled.

3. Open Central Administration -> go to your configured Shared Service -> click add new trusted file location
-Field URL: here you can specify a report library or the whole portal
-Location Type: should be Windows SharePoint Services
-Children trusted: defines whether the children should also be trusted or only the definied path