It's not the user name that needs to be the same, it's the account name. If you define identical account names with identical passwords in each file, you should only need to enter your account name and password once. Note that passwords are case sensitive so it is important to use exactly the same capitalization for each instance of the same password.
Account names are defined in Manage | Security. User names are defined in passwords. But the FileMaker confuses people by automatically entering the current user name as the default account name when the file is opened.
Thanks so much for the reply. I'm sorry, I should have been more clear.. yes, the Account Names are identical across all 15 files :(
For example the account name ‘press’, all lowercase is that same and also have the same password. Also, all referenced files have been added as External Data Sources and I have tried to check every other setting as well. I was hoping that was the purpose of the File Access tab in the Security set up.. to Authorize and Deauthorize access but that seems more to limit than to enable access. Hmmm…. Now what? A script that passes account name and password? Seems like a lot of work.
None of that should be necessary. What you have set up should work. I've used this method for years with many versions of FileMaker.
One way to simplify your set up would be to move all the tables into a single file instead of using separate files for this. That way, you only have one set of accounts and passwords to manage.