I’m not sure if this will help you out or not, but I ran into a similar situation this morning when trying to change the table prefix.
For me, it was a permission issue with the wp-config.php file on the server that was being masked by the “invalid format” issue.
What I did to get around this was to temporarily enable write access, as it wasn’t set for all accounts on the server.
Now, of course, this can lead to security vulnerabilities, as well, so I would say that after you finish your configuration, remove the ‘write’ permission, or restore the permissions back to whatever they were prior to the mod.
If that doesn’t work, then I’m not sure what else to suggest, as this fixed my problems.
Hope this helps,
Tony
