QB Issue Resolution:

first try making a back up to a local hard drive, QB does not play well with external drives

if that does not work, then In Desktop, back up the file then use the main menu File>Utilities>Rebuild and  run it as many times as necessary (but at least 3 times) until it completes, then run verify (if there are still errors run rebuild again), then close QB and re-open it and see if it helped

Resolution for Issue 'Backup data error' available: Yes (Solved).
Source: Intuit Community forum.

Backup data error: this issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the issue yourself by looking for a resolution described below. If it is a complex issue or you are unable to solve the issue, you may contact us by clicking here or by using other support options.

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