Event ID 9782 is thrown after successful backup

Challenge

During Exchange 2010 application aware backup with “Copy only” option enabled you notice following events in Application event log on Exchange server:

Log Name:      Application
Source:        MSExchangeIS
Date:          5/10/2018 5:38:39 PM
Event ID:      9782
Task Category: Exchange VSS Writer
Level:         Error
Keywords:      Classic
User:          N/A
Computer:      Exchange2010
Description:
Exchange VSS Writer (instance 7333fe6c-94b5-4d0f-b62f-517eec18e04d:2) has completed the backup of database '<Database name>' with errors. The backup did not complete successfully, and no log files were truncated for this database.
Event Xml:
<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
  <System>
    <Provider Name="MSExchangeIS" />
    <EventID Qualifiers="49193">9782</EventID>
    <Level>2</Level>
    <Task>41</Task>
    <Keywords>0x80000000000000</Keywords>
    <TimeCreated SystemTime="2018-05-10T14:38:39.000000000Z" />
    <EventRecordID>1801912</EventRecordID>
    <Channel>Application</Channel>
    <Computer><Server name></Computer>
    <Security />
  </System>
  <EventData>
    <Data>7333fe6c-94b5-4d0f-b62f-517eec18e04d:2</Data>
    <Data><Database name></Data>
    <Binary>436F707900</Binary>
  </EventData>
</Event>
 

Cause

Copy only backup does not perform transaction logs truncation which may result in the mentioned event being generated.

Solution

Event can be safely ignored.