You do not have permissions to open this file on Excel Services.

After updating which URLs SharePoint could be accessed with, I was getting an error on some Business Data Catalog (BDC) dashboards.

I was getting this error:

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

What fixed it for me was:
1: Go to Central Administration and click on the link to SharedServices1 or whatever you named it.

2: Under Excel Services Settings click Excel Services Trusted File Locations

3: Edit each line to reflect what URL you access sharepoint with.
In my case I went from servername like:
“http://codejourney”
To a FQDN like:
“http://sharepoint.code-journey.com”
On the SharePoint site at work I made sure there was only one URL that would work for SharePoint, but if you got multiple paths to get to SharePoint you will probably need to have trusted file locations set up for each URL.
For instance, I could have had a trusted file location for both “http://codejourney” and “http://sharepoint.code-journey.com”.

This did it for me but if you are manually adding excel files or the likes to BDC you might need to add a new trusted file location altogether instead of editing existing ones.
You can do this by clicking “Add Trusted File Location” under Trusted File Locations.
Specify the share or address for the BDC files. This could be “http://sharepoint.code-journey.com/itmanager”.