Direct from Jeffrey Siegel of Active Captain:

We received emails and comments from about a dozen people using Garmin BlueChart Mobile over the last day. It seems that they are having problems logging into their ActiveCaptain account. It might have to do with iOS 8.3 too although that's not verified.

I contacted Garmin and they've been looking into it today. It seems like there's an easy workaround. The problem is only happening on iPads. If you try to login and it just rejects the account and asks you to login again, rotate the screen, let the display flip, and try to login again. It should work in the rotated mode.

Please pass this info around if you here about any problems with logging into Garmin's app on iPads. Thanks to the Garmin engineers who stayed late looking into this.