QB Issue Resolution:

Nobody here can fix issues in your file. This is a peer user community and the problems are in your file, not anywhere else that someone can push a button or provide a system update to fix. It is likely a damaged template.

 

Try the steps in this post https://community.intuit.com/questions/1625905-i-keep-getting-error-code-c-387 and if that does not work use the contact support link provided

Resolution for Issue 'Unexpected Error' available: Yes (Solved).
Source: Intuit Community forum.

Unexpected 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.

Support for system update
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Error Recovery for system update [Canada]
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Additional Support Options: