I can't check in!

Here are the usual causes of check-in errors:

Weak or changing internet connection (offline support is a top request, but we don't have it at this time)
Time zone in Coach.me settings does not match the time zone set on the device (check Coach.me settings and also the settings on your device or computer)
On the iPhone, the Calendar setting is not set to Gregorian (check Settings --> General)
Also on the iPhone, having an Arabic selection for "International" (check Settings --> General)
Current versions of Coach.me require iOS 7 or above. If you are using an older version under the previous app name "Lift", you'll need to update.

If all else fails, iPhone and Android users should try removing the app and reinstalling it. Your data will still be there, and this often solves strange problems.