The Address Book custom properties couldn't be parsed. "%1" attribute wasn't found in "%2" at line number = "%3". Having ...

The Address Book custom properties couldn't be parsed. 

"%1" attribute wasn't found in "%2" at line number = "%3". Having the "%1" as the "%4" attribute in the custom properties file is a requirement for Outlook Web App to parse it and display the values to users. If this error isn't addressed, users won't be able to view the custom properties. The Help and Support Center provides information about how to troubleshoot this issue.