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I set Admin Base URL to admin/ (apparently a very bad idea) and now I can’t change it back the whole back end blew up. I can navigate to the place to change it but I can’t submit the changes. Is there any way to disable this without the back end? As you can see there seems to be no theme.
I seem to have this problem too (500 error for any /admin/ URL - it was working originally so I don’t know why it suddenly blew up!), but admin/url/use_custom and admin/url/custom do not seem to exist in my core_config_data table. The other two are already set to my base domain. My installation is 1.2.1. Front end and Magento connect manager seem to work fine.