Problems with Manager login

I'm running MODX Evo 1.0.15. Whenever I (or anyone else) tries to login to the Manager, we get a popup window with a blank error message: "The page at [url] says: Location: [url]." I click the OK button and I'm presented with the login screen again. For one particular manager user and one particular browser only (Chrome), I can get in by simply refreshing the page. It seems that the login is successful but MODX isn't properly redirecting the logged in user to the Manager home screen. The successful logins show up in the log.

Has anyone else experienced this? Does anyone have an idea of what might be happening here? I recently upgraded this site to 1.0.15 but it was several weeks before this started happening.