sorry

Use sorry (and similar wording) only in error messages that notify the customer about a serious problem or one that they might find very frustrating, such as:

• Data is lost.
• The customer can't continue to use the device, service, or application.
• The customer must get help from a support representative.
• A product or service fails.

Error messages should apologize only for things that went wrong with the Microsoft product. Don't apologize for problems that are outside the product, such as a broken link or waiting for a network connection to be found. Consider Oops or Hmm instead.

Examples
We're sorry, but we detected a problem, and your PC was shut down to protect your files and other data.
Sorry, the service isn't available right now.
This task couldn't be completed. Please try again.
You're not connected. Let's get you back online.
Hmm ... can't reach this page
Oops ... this page didn't load properly.
Let's try this again.