According to Intuit, Error Code -6000, -816 “QuickBooks was unable to open the company file because the file is in use” has multiple possible causes, at least 1 of which is unresolved and is associated with Microsoft Windows Vista. The possible causes of this error are:
- the company file is in use by another program such as third-party backup software
- a damaged company file (.qbw)
- the company file is located on a computer running Microsoft Windows Home Server edition with multiple hard disks (not supported)
- opening a company file (.qbw) or a restored company file on a computer running Vista (unresolved)
There is a possible workaround for the Vista-related issue discussed in the Intuit article linked below.
For more information on resolving Error Code -6000, -816, consult this Intuit knowledge base article.